Magnetic resonance imaging of bone marrow changes in Gaucher disease during enzyme replacement therapy: first German long-term results

Deep learning-based quantification of osteonecrosis using magnetic resonance images in Gaucher disease

Gaucher disease is one of the most common lysosomal storage disorders. Osteonecrosis is a principal clinical manifestation of Gaucher disease and often leads to joint collapse and fractures. T1-weighted (T1w) modality in MRI is widely used to monitor bone involvement in Gaucher disease and to diagnose osteonecrosis. However, objective and quantitative methods for characterizing osteonecrosis are still limited. In this work, we present a deep learning-based quantification approach for the segmentation of osteonecrosis and the extraction of characteristic parameters. We first constructed two independent U-net models to segment the osteonecrosis and bone marrow unaffected by osteonecrosis (UBM) in spine and femur respectively, based on T1w images from patients in the UK national Gaucherite study database. We manually delineated parcellation maps including osteonecrosis and UBM from 364 T1w images (176 for spine, 188 for femur) as the training datasets, and the trained models were subsequently applied to all the 917 T1w images in the database. To quantify the segmentation, we calculated morphological parameters including the volume of osteonecrosis, the volume of UBM, and the fraction of total marrow occupied by osteonecrosis. Then, we examined the correlation between calculated features and the bone marrow burden score for marrow infiltration of the corresponding image, and no strong correlation was found. In addition, we analyzed the influence of splenectomy and the interval between the age at first symptom and the age of onset of treatment on the quantitative measurements of osteonecrosis. The results are consistent with previous studies, showing that prior splenectomy is closely associated with the fractional volume of osteonecrosis, and there is a positive relationship between the duration of untreated disease and the quantifications of osteonecrosis. We propose this technique as an efficient and reliable tool for assessing the extent of osteonecrosis in MR images of patients and improving prediction of clinically important adverse events.

Bone marrow burden score is not useful as a follow-up parameter in stable patients with type 1 Gaucher disease after 5 years of treatment

INTRODUCTION

Gaucher disease (GD) is one of the most prevalent lysosomal disorders, with an estimated incidence of 1 in 40,000 live births worldwide. Skeletal involvement is one of the main features of GD, causing morbidity and impacting long-term quality of life in patients with type 1 GD.

OBJECTIVES

To characterize bone marrow infiltration in patients with type 1 GD followed at the Gaucher Disease Referral Center of Porto Alegre, Brazil, and to assess whether the Bone Marrow Burden score (BMB) correlates with clinical or laboratory parameters. We also evaluated whether the BMB score is a suitable parameter for long-term follow-up of patients with type 1 GD.

METHODS

All included patients underwent magnetic resonance imaging for BMB score calculation at baseline, 1 year, and every other year thereafter or as clinically indicated from 2012 to 2018.

RESULTS

The BMB score tended to decrease during the first 5 years of treatment, at a rate of -1.08 points per year; after the 5-year mark, BMB tended to remain stable.

CONCLUSIONS

The BMB score is useful for response monitoring in the first five years of treatment. We recommend that, after 5 years of treatment, MRI for BMB evaluation should only be performed in non-adherent patients or in those who develop symptoms of acute skeletal disease.

Successful treatment of Gaucher disease type 1 by enzyme replacement therapy over a 10-year duration in a Japanese pediatric patient: A case report

The prevalence of Gaucher disease (GD) in Japan is much lower than that in Western countries; therefore, data on Japanese pediatric patients with GD type 1 are currently limited. The present study reports on the case of a Japanese pediatric patient with GD type 1 who was diagnosed when she presented with hepatosplenomegaly, thrombocytopenia and slight anemia at the age of 2 years. Serology tests revealed high levels of acid phosphatase (ACP) and angiotensin-converting enzyme (ACE). A bone marrow biopsy revealed the presence of Gaucher cells. Abdominal MRI indicated huge hepatosplenomegaly. Erlenmeyer flask deformity was observed on X-ray examination. MRI of the femora featured a high-intensity area within the diaphysis region. The enzymatic activity of leukocyte β-glucosidase, the measurement of which is necessary for a definitive diagnosis of GD, had decreased to 186.7 nmol/h/mg (reference range, 1,424.0-2,338.0 nmol/h/mg). Based on these results, the patient was clinically diagnosed with GD. Glucocerebrosidase gene analysis identified the compound heterozygote mutation of F213I (c.754T>A) on exon 7 and L444P (c.1448T>C) on exon 11. Enzyme replacement therapy (ERT) along with an intravenous infusion of 60 U/kg of imiglucerase every other week was initiated following diagnosis. Hemoglobin levels and the platelet count gradually improved and normalized after two years. ACP and ACE levels, biomarkers of the progression of GD, also improved. Abdominal MRI at six months after the initiation of ERT revealed a decrease in the size of the liver and spleen, which normalized after 1 year. Conversely, MRI of the femora indicated no improvement in the high-intensity area within the diaphysis region for 10 years.

Gaucher Disease in Bone: From Pathophysiology to Practice

Gaucher disease (GD) is a rare, genetic lysosomal disorder leading to lipid accumulation and dysfunction in multiple organs. Involvement of the skeleton is one of the most prevalent aspects of GD and a major cause of pain, disability, and reduced quality of life. Uniform recommendations for contemporary evaluation and management are needed. To develop practical clinical recommendations, an international group of experienced physicians conducted a comprehensive review of 20 years' of the literature, defining terms according to pathophysiological understanding and pointing out best practice and unmet needs related to the skeletal features of this disorder. Abnormalities of bone modeling, reduced bone density, bone infarction, and plasma cell dyscrasias accompany the displacement of healthy adipocytes in adult marrow. Exposure to excess bioactive glycosphingolipids appears to affect hematopoiesis and the balance of osteoblast and osteoclast numbers and activity. Imbalance between bone formation and breakdown induces disordered trabecular and cortical bone modeling, cortical bone thinning, fragility fractures, and osteolytic lesions. Regular assessment of bone mineral density, marrow infiltration, the axial skeleton and searching for potential malignancy are recommended. MRI is valuable for monitoring skeletal involvement: It provides semiquantitative assessment of marrow infiltration and the degree of bone infarction. When MRI is not available, monitoring of painful acute bone crises and osteonecrosis by plain X-ray has limited value. In adult patients, we recommend DXA of the lumbar spine and left and right hips, with careful protocols designed to exclude focal disease; serial follow-up should be done using the same standardized instrument. Skeletal health may be improved by common measures, including adequate calcium and vitamin D and management of pain and orthopedic complications. Prompt initiation of specific therapy for GD is crucial to optimizing outcomes and preventing irreversible skeletal complications. Investing in safe, clinically useful, and better predictive methods for determining bone integrity and fracture risk remains a need. © 2019 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

DOENÇA DE GAUCHER TIPO 1 NO ESQUELETO: REVISÃO DA AMÉRICA LATINA

RESUMO A doença de Gaucher (DG) é a doença de depósito lisossômico mais prevalente, que se caracteriza pelo acúmulo de glicosilceramida e glucosilesfingosina em todos os tecidos do corpo. Com o advento da terapia de reposição de enzimas, o prognóstico dos pacientes com DG melhorou acentuadamente. Ainda assim, as manifestações esqueléticas associadas à DG respondem lentamente à terapia de reposição de enzimas e são as que contribuem de forma mais significativa para a morbidade do paciente. Esta revisão das manifestações ósseas da DG apresenta as mais recentes teorias sobre a sua fisiopatologia e uma revisão sistemática de estudos com pacientes latino-americanos que relataram a frequência das manifestações ósseas e os efeitos da terapia de reposição de enzimas sobre seu tratamento. Concluímos, destacando a importância da identificação precoce e do manejo adequado das doses apropriadas da terapia de reposição de enzimas para reduzir a morbidade causada pela DG.

Skeletal involvement in Gaucher disease: An observational multicenter study of prognostic factors in the Argentine Gaucher disease patients

Patients with Gaucher type 1 (GD1) throughout Argentina were enrolled in the Argentine bone project to evaluate bone disease and its determinants. We focused on presence and predictors of bone lesions (BL) and their relationship to therapeutic goals (TG) with timing and dose of enzyme replacement therapy (ERT). A total of 124 patients on ERT were enrolled in a multi-center study. All six TG were achieved by 82% of patients: 70.1% for bone pain and 91.1% for bone crisis. However, despite the fact that bone TGs were achieved, residual bone disease was present in 108 patients on ERT (87%) at time 0. 16% of patients showed new irreversible BL (bone infarcts and avascular osteonecrosis) despite ERT, suggesting that they appeared during ERT or were not detected at the moment of diagnosis. We observed 5 prognostic factors that predicted a higher probability of being free of bone disease: optimal ERT compliance; early diagnosis; timely initiation of therapy; ERT initiation dose ≥45 UI/kg/EOW; and the absence of history of splenectomy. Skeletal involvement was classified into 4 major phenotypic groups according to BL: group 1 (12.9%) without BL; group 2 (28.2%) with reversible BL; group 3 (41.9%) with reversible BL and irreversible chronic BL; and group 4 (16.9%) with acute irreversible BL. Our study identifies prognostic factors for achieving best therapeutic outcomes, introduces new risk stratification for patients and suggests the need for a redefinition of bone TG. Am. J. Hematol. 91:E448-E453, 2016. © 2016 Wiley Periodicals, Inc.

Standardization of MRI and Scintigraphic Scores for Assessing the Severity of Bone Marrow Involvement in Adult Patients With Type 1 Gaucher Disease

OBJECTIVE

MRI and (99m)Tc-sestamibi scintigraphy are used to estimate bone marrow infiltration in patients with Gaucher disease (GD), but comparison of data obtained at different institutions is difficult because different scores are employed for semiquantitative assessment. We developed normalized scores for comparing data both within a single method (MRI) and between different methods (MRI versus scintigraphy).

MATERIALS AND METHODS

We evaluated 51 patients with type 1 GD (26 women, 25 men; mean age ± SD, 36.3 ± 10.9 years old). T1- and T2-weighted turbo spin-echo sequences at 1.5 T served to derive the bone marrow burden score (0-16), the vertebra-disk ratio (VDR), the Terk score (0-3), and the Spanish-MRI score (S-MRI, 0-24). Scintigraphy was scored between 0 and 8. Each score was normalized into four categories: 0 = normal, 1 = mild, 2 = intermediate, 3 = severe involvement. Interobserver and intraobserver agreements were evaluated by kappa statistics; nonparametric statistics with Bonferroni correction assessed correlations among the various original and normalized scores.

RESULTS

Interobserver agreement was excellent for the original scores (κ = 0.730-0.843) and even more so for the normalized scores (κ = 0.775-0.940). Intraobserver agreement kappa values ranged from 0.753 to 0.937 for the original scores and 0.851 to 1.000 for the normalized scores. Highly significant correlations were found among the various original scores (r = 0.42-0.86, p values between 0.0296 and < 0.0001), except for VDR versus S-MRI and Terk. Normalization generally induced marginal reductions in statistical significance, whereas S-MRI versus VDR reached statistical significance with the normalized scores.

CONCLUSION

Our data indicate no significant loss of statistical information is caused by the normalization we employed. Our approach therefore facilitates comparison of different scores obtained in different institutions with different imaging modalities.

Magnetic resonance imaging and BMB score in the evaluation of bone involvement in Gaucher's disease patients

Objective

To evaluate by magnetic resonance imaging changes in bone marrow of patients undergoing treatment for type I Gaucher’s disease.

Materials and Methods

Descriptive, cross-sectional study of Gaucher’s disease patients submitted to 3 T magnetic resonance imaging of femurs and lumbar spine. The images were blindly reviewed and the findings were classified according to the semiquantitative bone marrow burden (BMB) scoring system.

Results

All of the seven evaluated patients (three men and four women) presented signs of bone marrow infiltration. Osteonecrosis of the femoral head was found in three patients, Erlenmeyer flask deformity in five, and no patient had vertebral body collapse. The mean BMB score was 11, ranging from 9 to 14.

Conclusion

Magnetic resonance imaging is currently the method of choice for assessing bone involvement in Gaucher’s disease in adults due to its high sensitivity to detect both focal and diffuse bone marrow changes, and the BMB score is a simplified method for semiquantitative analysis, without depending on advanced sequences or sophisticated hardware, allowing for the classification of the disease extent and assisting in the treatment monitoring.

Bone marrow involvement in Gaucher disease at MRI : what long-term evolution can we expect under enzyme replacement therapy?

PURPOSE

To study the long-term evolution of the bone marrow burden (BMB) score at MRI in patients with Gaucher disease (GD) under enzyme replacement therapy (ERT).

MATERIAL AND METHODS

Forty patients treated for GD were retrospectively studied in a referral centre. BMB scores were assessed on spine and femur MR examinations performed between January 2003 and June 2014. The long-term evolution of the BMB scores was analyzed using a linear mixed model.

RESULTS

A total of 121 MRI examinations were performed during the study period with a mean follow-up of 7.1 years ± 5.6, an average rate of 3.1 MR examinations ± 1.7 per patient and an interval of 2.3 years ± 1.1 between examinations. Patients had received ERT during 12 years on average ± 6.7. The trend of BMB scores with time decreased significantly by 15% (P = 0.008) during the total study period and 39% (P = 0.01) during the first 5 years of treatment. No changes in BMB scores were observed after five years of treatment.

CONCLUSION

In Gaucher patients, the trend of MRI BMB scores with time decreased significantly under ERT the first 5 years of treatment before a long-term stabilization.

KEY POINTS

• Bone marrow infiltration of Gaucher patients responds to enzyme replacement therapy • MRI BMB score decreases mainly during the first five years of treatment • MRI BMB score tends to stabilize after five years of treatment • MR examinations could be limited after five years of treatment.

Evaluation of bone involvement in patients with Gaucher disease: a semi-quantitative magnetic resonance imaging method (using ROI estimation of bone lesion) as an alternative method to semi-quantitative methods used so far

OBJECTIVE

The aim of this study was to evaluate bone involvement in patients with Gaucher disease (GD) and to propose a novel semi-quantitative magnetic resonance imaging (MRI) staging.

METHODS

MRI of the lumbar spine, femur, and tibia was performed in 24 patients with GD and 24 healthy controls. We also measured circulating levels of C-C motif ligand-3 (CCL-3) chemokine, C-telopeptide of collagen type-1 (CTX), and tartrate-resistant acid phosphatase isoform type-b (TRACP-5b).

RESULTS

We used the following staging based on MRI data: stage I: region of interest (ROI) 1/2 of normal values and bone infiltration up to 30%; stage II: ROI 1/3 of normal values and bone infiltration from 30 to 60%; stage III: ROI 1/4 of normal values and bone infiltration from 60% to 80%; and stage IV: detection of epiphyseal infiltration, osteonecrosis and deformity regardless of the ROI's values. All but two patients had abnormal MRI findings: 9 (37.5%), 6 (25%), 3 (12.5%), and 4 (16.7%) had stages I-IV, respectively. Patients with GD had elevated chitotriosidase, serum TRACP-5b, and CCL-3 levels (P < 0.001).

CONCLUSIONS

We propose an easily reproducible semi-quantitative scoring system and confirm that patients with GD have abnormal MRI bone findings and enhanced osteoclast activity possibly due to elevated CCL-3.

Innovative treatments for lysosomal diseases

Striking therapeutic advances for lysosomal diseases have harnessed the biology of this organelle and illustrate its central rôle in the dynamic economy of the cell. Further Innovation will require improved protein-targetting or realization of therapeutic gene- and cell transfer stratagems. Rescuing function before irreversible injury, mandates a deep knowledge of clinical behaviour as well as molecular pathology – and frequently requires an understanding of neuropathology. Whether addressing primary causes, or rebalancing the effects of disordered cell function, true therapeutic innovation depends on continuing scientific exploration of the lysosome. Genuine partnerships between biotech and the patients affected by this extraordinary family of disorders continue to drive productive pharmaceutical discovery.

Management of bone disease in Gaucher disease type 1: clinical practice

Gaucher disease is a rare autosomal recessive disorder of glycosphingolipid metabolism resulting from deficient activity of the lysosomal enzyme beta-glucocerebrosidase that causes accumulation of glucosylceramide in tissue macrophage with damage to hematological, visceral, and skeletal organ systems. Severity and progression may vary independently among these domains, necessitating individualized therapy. Skeletal involvement is highly prevalent and often associated with intense pain, impaired mobility, and reduced quality of life. Enzyme replacement therapy improves parameters in all affected domains, but skeletal involvement requires longer treatment and higher dosages to obtain significant results. Despite numerous papers on bone complications in patients with Gaucher disease, there are no specific indications on how to assess properly bone involvement in such condition, the frequency of assessment, the use of markers for osteoblast and osteoclast activity, or the administration of bisphosphonates or other symptomatic drugs in adult and pediatric patients. Starting from a re-evaluation of cases with bone involvement, we have identified some common errors in the diagnostic approach and management. The aim of this paper was to propose a methodological and critical approach to the diagnosis, follow-up and treatment of bone disease in patients with Gaucher disease type 1.

Skeletal improvement in patients with Gaucher disease type 1: a phase 2 trial of oral eliglustat

OBJECTIVE

Eliglustat is an investigational oral substrate reduction therapy for Gaucher disease type 1 (GD1). Its skeletal effects were evaluated by prospective monitoring of bone mineral density (BMD), fractures, marrow infiltration by Gaucher cells, focal bone lesions, and infarcts during an open-label, multi-site, single-arm phase 2 trial (NCT00358150).

MATERIALS AND METHODS

Institutional review board approval and patient informed consent were obtained. Eliglustat (50 or 100 mg) was self-administered by mouth twice daily; 19 patients completed 4 years of treatment. All were skeletally mature (age range, 18-55 years). DXA and MRI assessments were conducted at baseline and annually thereafter. X-rays were obtained annually until month 24, and then every other year.

RESULTS

Lumbar spine BMD increased significantly (p = 0.02; n = 15) by a mean (SD) of 9.9% (14.2%) from baseline to year 4; corresponding T-scores increased significantly (p = 0.01) from a mean (SD) of -1.6 (1.1) to -0.9 (1.3). Mean femur T-score remained normal through 4 years. Femur MRI showed that 10/18 (56%) patients had decreased Gaucher cell infiltration compared to baseline; one patient with early improvement had transient worsening at year 4. There were no lumbar spine or femoral fractures and no reported bone crises during the study. At baseline, 8/19 (42%) patients had focal bone lesions, which remained stable, and 7/19 (37%) patients had bone infarctions, which improved in one patient by year 2. At year 4, one new asymptomatic, indeterminate bone lesion was discovered that subsequently resolved.

CONCLUSIONS

Eliglustat may be a therapeutic option for treating the skeletal manifestations of GD1.

Imaging of Gaucher disease

Gaucher disease is the prototypical lysosomal storage disease. It results from the accumulation of undegraded glucosylceramide in the reticuloendothelial system of the bone marrow, spleen and liver due to deficiency of the enzyme glucocerebrosidase. This leads to hematologic, visceral and skeletal maifestions. Build up of glucosylceramide in the liver and spleen results in hepatosplenomegaly. The normal bone marrow is replaced by the accumulating substrate leading to many of the hematologic signs including anemia. The visceral and skeletal manifestations can be visualized with various imaging modalities including radiography, computed tomography, magnetic resonance imaging (MRI) and radionuclide scanning. Prior to the development of enzyme replacement therapy, treatment was only supportive. However, once intravenous enzyme replacement therapy became available in the 1990s it quickly became the standard of care. Enzyme replacement therapy leads to improvement in all manifestations. The visceral and hematologic manifestations respond more quickly usually within a few months or years. The skeletal manifestations take much longer, usually several years, to show improvement. In recent years newer treatment strategies, such as substrate reduction therapy, have been under investigation. Imaging plays a key role in both initial diagnosis and routine monitoring of patient on treatment particularly volumetric MRI of the liver and spleen and MRI of the femora for evaluating bone marrow disease burden.

Modelling Gaucher disease progression: long-term enzyme replacement therapy reduces the incidence of splenectomy and bone complications

Long-term complications and associated conditions of type 1 Gaucher Disease (GD) can include splenectomy, bone complications, pulmonary hypertension, Parkinson disease and malignancies. Enzyme replacement therapy (ERT) reverses cytopenia and reduces organomegaly. To study the effects of ERT on long-term complications and associated conditions, the course of Gaucher disease was modelled.

The cohort consisted of all diagnosed GD patients in the Netherlands. Mutually exclusive disease states were defined as ‘asymptomatic’, ‘signs/symptoms’, ‘recovery’, ‘splenectomy’, ‘bone complication’, ‘multiple complications’ and ‘malignancy’. A natural history (NH) cohort was delineated based upon historical data on Dutch patients before ERT was available. Cumulative incidence curves were composed for progression from each disease state to the next. Two scenarios were applied for the ERT cohort: time to complications was calculated from A. start of ERT; B. entering the previous disease state.

Median time for the development of signs and/or symptoms was 30.1 years (N = 73). In the NH cohort (N = 42), 9% had developed a bone complication after 10 years in the signs/symptoms phase, while 21% had undergone a splenectomy. In the ERT cohort (N = 29 (A), N = 28 (B)), 12% (A) or 4% (B) had developed a bone complication after 10 years in this phase and no patient was splenectomized. No patients in the NH cohort recovered, compared to 50% in the ERT cohort after 3.6 years (N = 28 (A)) or 22.4 years (N = 27 (B)) of treatment. Median time from a first to a second complication was 11 years in the NH cohort (N = 31), whereas 16 respectively 14 percent had developed a second complication after 10 years in the ERT cohort (N = 17, scenario A/B). Fourteen percent (scenario A/B) developed an associated malignancy after 10 years in the phase ‘multiple complications’ (N = 23). Associated malignancies occurred almost exclusively in advanced disease stages, therefore it is suggested that ERT reduces their incidence

Long-term ERT for GD can reduce the incidence of splenectomy and bone complications. As ERT prevents progression to more advanced stages of GD it will most likely result in a reduction of associated malignancies.

Gaucher disease: a diagnostic challenge for internists

Gaucher disease (GD), the most common inherited lysosomal storage disorder, is a multiorgan disease due to an autosomal recessive defect of the gene encoding glucocerebrosidase enzyme, responsible for the accumulation of glucosylceramide (glucocerebroside) into reticuloendothelial cells, particularly in the liver, spleen and bone marrow. GD is a clinically heterogeneous disorder and it is conventionally classified in type 1 (non-neuronopathic disease), types 2 and 3 (acute and chronic neuronopathic disease, respectively). Features of clinical presentation and organ involvement as well as age, at presentation are highly variable among affected patients. Splenomegaly and/or thrombocytopenia are the most common presenting features either as incidental findings during routine blood count or physical examination. Other possible clinical manifestations can be hepatomegaly with abnormal liver function tests, bone pain often associated with skeletal complications (pathological fractures, avascular necrosis, osteopenia), pulmonary hypertension and, in neuronopathic forms, neurological manifestations (dysfunction of eye motility, mild mental retardation, behavioural difficulties, choreoathetosis and cramp attacks). For all these reasons GD diagnosis is often a real challenge for internists. In the presence of clinical suspicion of GD, the diagnosis has to be confirmed measuring the betaglucocerebrosidase activity in the peripheral leukocytes and by molecular analysis. Each patient needs an accurate initial multisystemic assessment, staging the damage of all the possible organs involved, and the burden of the disease, followed by regular followup. The correct and early diagnosis permits to treat patients properly, avoiding the complications of the disease.

Minimal disease activity in Gaucher disease: criteria for definition

Gaucher disease type I is a metabolic disorder caused by a genetic deficiency of lysosomal β-glucocerebrosidase that leads to accumulation of glucocerebroside in macrophages, thus causing damage in different organ systems. Enzyme replacement therapy with imiglucerase improves organ impairment and clinical manifestations, but patients differ in response to treatment. While clinical remission is the most desirable therapeutic outcome, a more realistic goal in patients with high disease burden is reasonably good clinical status despite persistence of residual biochemical or imaging abnormalities. Therefore, the concept of minimal disease activity--used in certain haematological or rheumatologic conditions--needs to be introduced in Gaucher disease, with a level of disease activity that patients and physicians consider a useful treatment target. In this paper, we propose specific parameters and criteria for defining minimal disease activity in Gaucher disease and its stability over time, based on three major systemic domains typically involved: haematological, visceral, and skeletal. Biomarker parameters were not included as criteria, because currently they do not adequately reflect disease evolution in individual patients. Neurological and respiratory domains were also excluded, as their involvement per se indicates severe disease unlikely to respond to enzyme replacement therapy and achieve minimal disease status. Our goal in defining minimal disease activity and stability is to identify a tool to facilitate treatment decisions in clinical practice.

Miscellaneous non-inflammatory musculoskeletal conditions. Gaucher disease and bone

Gaucher disease (GD) is an inherited lysosomal storage disorder affecting multiple organs. Non-neuronopathic GD, the most common form, can present with hepatosplenomegaly, anaemia, bleeding tendencies, thrombocytopenia, skeletal pathologies, growth retardation and, in severe cases, with pulmonary disease. The bone manifestations include bone infarcts, avascular bone necrosis, lytic lesions, osteosclerosis, fractures due to osteoporosis and, rarely, acute osteomyelitis. Bone pain of varying intensity, fractures and joint collapses increase the patients' morbidity and impair their mobility and quality of life. Currently available therapies - enzyme replacement therapy and substrate reduction therapy - have shown to improve blood count and the visceral manifestations within a short time. Beneficial effects have also been documented on bone pain, bone crises and the extent of osteoporosis. The article focusses on the bone pathologies of GD including its pathophysiology, current diagnostics, clinical management and therapeutic effects of enzyme replacement therapy, substrate reduction therapy and bone-specific therapies.

Substrate reduction therapy with miglustat for type 1 Gaucher disease: a retrospective analysis from a single institution

INTRODUCTION

Gaucher disease (GD) is an infrequent progressive multisystem lysosomal storage disorder caused by the deficient activity of the lysosomal enzyme, glucocerebrosidase. A retrospective, single-center analysis of the clinical experience concerning the use of miglustat (N-butyldeoxynojirimycin), an oral inhibitor of glucosylceramide synthase, in type 1 Gaucher disease (GD1) was conducted to evaluate the efficacy, adverse events (AE), and outcome of miglustat therapy.

PATIENTS AND METHODS

Six adult Caucasian patients with GD1 (two women and four men), aged 21-81 years (median age 59 years), were treated with miglustat between October 2005 and April 2011. All but one patient (83%) carried at least one allele with c.1226A>G (N370S) mutation in the GBA1 gene.

RESULTS

Weight loss, diarrhea, poor appetite, and tremor were frequently reported AE by the patients. All of them experienced at least 2 AE, and three patients (50%) experienced at least 4 AE. Only two out of six patients (33%) have used miglustat longer than 12 months, of which only one used it longer than 15 months.

CONCLUSIONS

The major obstacle to successful miglustat therapy in GD1 was the high proportion of patients discontinuing their treatment due to the AE and the worsened quality of life. Further efforts are needed to improve tolerability of miglustat and, in consequence, compliance of patients treated with this orphan drug.

Therapeutic approaches to bone pathology in Gaucher disease: past, present and future

Enzyme replacement therapy (ERT) is effective for the treatment of the systemic manifestations of Gaucher disease (GD) and can have a significant impact on skeletal manifestations. Bone involvement is broad and can occur in otherwise clinically asymptomatic individuals. The heterogeneity in GD-related bone disease may implicate multiple pathological processes such as disruption of coordinated bone cell activity, in addition to the physical impact of Gaucher cells causing vascular occlusion. Accumulated data suggests that earlier treatment initiation decreases skeletal complications and that bone disease may require a longer duration of treatment and higher dose than is necessary for organ involvement and hematopoietic manifestations. However, in some patients, bone manifestations persist and even worsen despite ERT, regardless of dose or duration of treatment. Treating skeletal disease should be considered of equal importance as treating visceral and hematologic manifestations. When treatment decisions involve multiple enzyme preparations and other therapeutic modalities such small molecules, the choice should be tailored on an individual basis with continuing evaluation.

Radiological aspects of Gaucher disease

Advances in imaging and the development of commercially available enzyme therapy have significantly altered the traditional radiology of Gaucher disease. The cost of treatment and need for monitoring response to therapy have magnified the importance of imaging. There are no recent comprehensive reviews of the radiology of this relatively common lysosomal storage disease. This article describes the modern imaging, techniques and radiological manifestations of Gaucher disease.

Gaucher disease: a systematic review and meta-analysis of bone complications and their response to treatment

Type 1 Gaucher disease (GD1) is an inherited lysosomal storage disease, which is often managed by enzyme replacement therapy (ERT). The bone response to ERT is usually slower than visceral and hematological responses. There is uncertainty as to whether an increase in the dosage of ERT has a beneficial effect. The aim of our study was to determine whether or not there is sufficient evidence to make a definitive statement about the effects of ERT and substrate reduction therapy (SRT) on bone marrow infiltration and bone mineral density (BMD) in GD1. We conducted a systematic review of all studies examining the effects of ERT and SRT on bony complications of GD1 published before July 2008. The studies were identified by a computerized search with use of Medline, Embase, The Cochrane Database of Systematic Reviews, The Cochrane Central Register of Controlled Trials (CCTR), and bibliographies of papers subsequently retrieved from the search. Three hundred studies were grouped according to whether they deal with the natural history of GD1 or therapeutic issues, and 17 studies were included in the review. The results from our systematic review suggest that further investigations, such as better analysis of the Gaucher Registry, are needed on the effects of ERT and SRT on bony complications of GD1. Studies on the effects of the newly identified velaglucerase and the plant-derived glucocerebrosidase on bony complications of GD1 are also needed.

The clinical course of untreated Gaucher disease in 22 patients over 10 years: hematological and skeletal manifestations

Gaucher disease (GD) is a lysosomal storage disorder characterized by anemia and thrombocytopenia, hepatosplenomegaly, and skeletal involvement. The management of Gaucher disease was improved by the development of enzyme replacement therapy (ERT). However, the bone response to ERT is generally slower compared to other clinical manifestations. Some have recommended the early use of ERT to prevent the development of severe skeletal complications. Because we have access to over 30 untreated patients in Ontario, we questioned the extent to which complications progress in severity over a long period of time. We examined retrospectively the natural history of GD and the extent of skeletal manifestations in 22 untreated type 1 GD adult patients (mean age, 49+/-3.3; range, 20-81 years). The patients were followed for a median of 9.5 years (range, 3-16 years). Hemoglobin (Hb) concentration did not significantly change over time (mean baseline concentration of 12.8+/-0.27 g/dL vs. mean recent concentration of 12.6+/-0.37 g/dL, p=0.65). Mean platelet count also remained relatively stable over time (mean baseline count of 138+/-13x10(9)/L vs. mean recent count of 138.5+/-18x10(9)/L, p=0.98). Mean ferritin and ACE concentrations were elevated and were stable over time. Liver volumes decreased over time (mean baseline liver volume of 1.2xnormal (N) vs. mean recent volume of 1.06xN, p=0.27) and 6 of 22 (27%) patients had moderate hepatomegaly (liver volume, 1.25-2.5xN). Spleen volumes remained stable over time (mean baseline spleen volume of 6.6xN vs. mean recent volume of 5.2xN, p=0.5). None of the changes was statistically significant. Four of 20 (20%) patients had moderate splenomegaly (spleen volume, 5-15xN), 2 of 20 (10%) had marked splenomegaly (spleen volume, >or=15xN), and 2 of 22 (9%) had had splenectomy. The most common skeletal manifestations were infiltration of the bone marrow in 16 of 22 (73%) patients followed by osteopenia in 15 of 22 (68%), Erlenmeyer flask deformity in 13 of 22 (59%), and infarctions in 6 of 22 (27%) patients. We observed that bone disease remained relatively stable over time in most patients, although three patients developed new infarcts over time, one developed an avascular necrosis (AVN), and four had an increase in the degree of osteopenia. Although GD and its skeletal complications progress in severity in some patients, our results suggest that GD complications, including bony disease, may stabilize over time. Therefore, early use of ERT may not be necessary in all type 1 GD patients.

A cross-sectional, mono-centric pilot study of insulin resistance in enzyme replacement therapy patients with Gaucher type I without overweight

Insulin resistance have been demonstrated in untreated patients with Gaucher type I disease. It was implied in overweight enzyme replacement therapy (ERT) treated patients with Gaucher type I disease. In present study we investigate whether insulin resistance is presented in fourteen ERT treated patients with Gaucher type I disease and without overweight in comparison to normal subjects. This work illustrates the presence of insulin resistance in non-overweight ERT treated patients with Gaucher type I disease.

Changes of bone metabolism in seven patients with Gaucher disease treated consecutively with imiglucerase and miglustat

Bone manifestations are frequent in Gaucher disease (GD), the most prevalent lysosomal storage disorder. Currently, therapy with enzyme replacement (ERT) or substrate reduction (SRT) is available. We investigated changes of laboratory parameters associated with bone metabolism in GD patients switching from ERT to SRT. Seven GD patients consecutively treated with ERT and SRT were studied. All patients had different degrees of bone involvement. Laboratory results were acquired at the time of change from ERT to SRT (0 months) and while on SRT (6 months, 12-18 months). Markers of GD activity remained stable or showed statistically insignificant increases. Six patients had stable skeletal manifestations and reported no bone-associated symptoms. One patient presented progressive bone manifestations on magnetic resonance imaging and experienced increasing bone pain. Osteocalcin, alkaline phosphatase, and C-terminal telopeptide of collagen I were initially within the lower part of the normal range and decreased during SRT (alkaline phosphatase P = 0.0169, osteocalcin nonsignificant, C-terminal telopeptide of collagen I nonsignificant). Tartrate-resistant acid phosphatase 5b was initially normal or slightly increased, and macrophage colony-stimulating factor was within the normal lower range; both parameters remained stable. Interleukin-6 was elevated only in the patient with progressive bone disease. Macrophage inflammatory protein 1alpha (MIP-1alpha) was elevated without change after switching to SRT. MIP-1beta was within the normal range, and no values were above 85 ng/mL, indicative of active skeletal disease. From a clinical and metabolic point of view, most skeletal manifestations and bone-associated laboratory parameters remain stable after switch from ERT to SRT.

Management of non-neuronopathic Gaucher disease with special reference to pregnancy, splenectomy, bisphosphonate therapy, use of biomarkers and bone disease monitoring

Enzyme replacement was introduced as treatment for non-neuronopathic Gaucher disease more than 15 years ago. To ensure the best use of this costly ultra-orphan agent, a systematic disease management approach has been proposed by an international panel; this includes the development, by consensus, of achievable treatment goals. Here we critically review these goals and monitoring guidelines and incorporate emerging experience of the disease in the therapeutic era, as well as contemporary clinical research. This review makes recommendations related specifically to the management of pregnancy; the appropriate use of splenectomy and bisphosphonate treatment; the relevance of biochemical markers to disease monitoring; and the use of semi-quantitative methods for assessing bone marrow infiltration. In addition, we identify key areas for development, including the requirement for a validated index of disease severity; the need to correlate widely used biomarkers with long-term disease outcomes, and the desirability of establishing agreed standards for monitoring of bone disease particularly in infants and children with Gaucher disease.

Atteintes ostéoarticulaires de la maladie de Gaucher chez l'adulte: de la physiopathologie au traitement

Gaucher disease frequently has severe osteoarticular manifestations that may be disabling. Ischemic phenomena cause the most serious complications and lead to irreversible lesions. Aseptic osteonecrosis of the hip is the most disabling complication; it causes intense early bone pain and often joint collapse and secondary osteoarthritis in young adults. Localized or systemic bone fragility explains osteopenia, osteoporosis, and fractures (vertebral collapse with irreversible kyphosis causing chronic morbidity). Although no double-blind randomized studies have assessed the bone effects of enzyme replacement therapy, it has been shown effective in reducing bone pain in about half of all treatment-naive patients within 1 to 2 years and in improving bone mineral density after 3 years. In open-label trials, substrate reduction therapy (miglustat) reduced both bone pain and bone marrow infiltration. Specific treatment for bone fragility, with bisphosphonates for example, should be considered after rigorous individualized evaluation and assessment of other risk factors.

The outcome of clinical parameters in adults with severe Type I Gaucher disease using very low dose enzyme replacement therapy

Enzyme replacement therapy is now well established as the treatment of choice in Type I Gaucher disease. Historically higher dosage regimens have been used in preference to lower doses despite the little clinical evidence in the way of large controlled clinical trials to support this. Moreover, the extraordinary cost of therapy means that not all eligible patients are able to be treated at the higher dose. Twelve type I adult patients with relatively severe disease were commenced on a very low dose of 7.5U of alglucerase/imiglucerase per kg every two weeks (initially given thrice weekly and later weekly). Follow-up 5 year data reveal a good visceral and haematological response with outcomes consistent with recently published treatment guidelines. Satisfactory clinical and radiological skeletal improvement was also demonstrated in most patients. Three patients had an inadequate overall skeletal response to therapy. Biomarkers also steadily improved although perhaps not quite at the same rate as that seen in higher doses. Very low dose enzyme replacement therapy may be appropriate for adult type I Gaucher patients with mild-moderate skeletal disease.

Semiquantitative assessment of skeletal response to enzyme replacement therapy for Gaucher's disease using the bone marrow burden score

OBJECTIVE

The purpose of this study was to evaluate the use of a recently described assessment tool to quantify bone marrow response to enzyme replacement therapy in a cohort of adult patients with type 1 Gaucher's disease.

MATERIALS AND METHODS

Serial MR images of the femurs, lumbar spine, or both of 57 subjects with a diagnosis of Gaucher's disease, 44 of whom were being treated with enzyme replacement therapy, were evaluated by two musculoskeletal radiologists using the bone marrow burden (BMB) scoring system. This system gives a score out of a possible 8 for the lumbar spine and a score out of a possible 8 for the femurs, so the total BMB score is out of 16.

RESULTS

The mean total BMB scores at baseline and final measurement were 13 (95% CI, 12.0-13.8) and 6.5 (95% CI, 5.2-7.9), respectively. Total BMB scores improved by 2-12 points (mean, 6.3 points) for 15 subjects in whom total BMB scores obtained before enzyme replacement therapy and at least one time point after commencement of therapy were available. In 39 subjects for whom only baseline and final femoral BMB scores were available, 24 subjects (62%, 95% CI, 47-76%) improved by 2 or more points while on enzyme replacement therapy. In 24 subjects for whom only baseline and final lumbar BMB scores were available, the BMB score in 16 subjects (67%, 95% CI, 48-85%) improved by 2 or more points.

CONCLUSION

The use of the BMB score enabled semiquantitative assessment of bone marrow response to enzyme replacement therapy in adult patients with type 1 Gaucher's disease in Australia. The ability to assess therapy response will facilitate the tailoring of dosage regimens in the future.

[Morbus gaucher--a report of two cases]

BACKGROUND

[corrected] Clinical features of inherited glucocerebrosidase deficiency were first described by Phillippe Charles Ernest Gaucher, French physician (1854-1918). Deficiency of glucocerebrosidase leads to the accumulation of the lipid glucocerebroside within the lysosomes of the monocyte macrophage system. Lipid-laden cells, known as Gaucher cells, lead to hepatosplenomegaly, multiorgan dysfunction and sceletal deterioration.

CASE REPORT

We reported a 36-year-old male and a 42-year-old female admitted for the clinical examination due to hepatosplenomegaly. The Clinical diagnosis was provided by a bone marrow examination and demonstration of the characteristic Gaucher cells. Both of the patients had type I Gaucher's disease (a mild form of the disease), wich is distiguished by the lack of central nervous system involvement and striking phenotypic variation. We had not a possibility of testing beta-glucocerebrosidase activity in peripheral leukocytes (a definitive diagnosis of Gaucher's disease). Also, enzyme replacement therapy had not been available in our country.

CONCLUSION

Althoungh rare, Gaucher's disease is also present in our country. Both molecular genetic, and the enzyme beta-glucocerebrosidase activity testing in peripheral leukocytes are needed for the definitive diagnosis of this disease.

S-MRI score: A simple method for assessing bone marrow involvement in Gaucher disease

Semi quantitative MRI is a very useful procedure for evaluating the bone marrow burden (BMB) in Gaucher disease (GD). Score systems have been applied to obtain a parameter for evaluating the severity of bone disease. Our purpose was to test a simple, reproducible and accurate score to evaluate bone marrow involvement in GD patients. MRI was performed in spine, pelvis and femora at diagnosis in 54 adult GD1 patients, 61.1% of whom were female. Three MRI patterns and punctuation in each location were defined: normal, 0; non-homogeneous infiltration subtypes reticular, 1; mottled, 2; diffuse, 3; and homogeneous infiltration, 4. This score was called Spanish-MRI (S-MRI). Two independent observers applied the S-MRI and bone marrow burden score and compared the differences using the non-parametric Mann-Whitney test. Correlation rank test was calculated. In 46 patients (85.2%), bone involvement was observed. Thirty-nine (72.3%) had their spine affected, 35 (64.8%) pelvis and 33 (61.2%) femora. Fourteen patients had bone infarcts, 14 avascular necrosis, 2 vertebral fractures and 2 bone crises. Correlation analysis between S-MRI and BMB was (r(2)=.675; p=.0001). No evidence of correlation was observed between CT activity and S-MRI nor between CT activity and BMB. We have found a relationship between genotype and bone infiltration according to S-MRI site and complications. S-MRI is a simple method that provides useful information to evaluate bone infiltration and detect silent complications. Our results correlated with the BMB score but offer higher sensitivity, specificity and accuracy for classifying the extent of bone disease.

New therapeutic options for lysosomal storage disorders: enzyme replacement, small molecules and gene therapy

During the last few years, much progress has been made in the treatment of lysosomal storage disorders. In the past, no specific therapy was available for the affected patients, and management consisted solely of supportive care and treatment of complications. Since enzyme replacement therapy has been successfully introduced for patients with Gaucher disease, this principle of treatment has been taken into consideration for other lysosomal storage disorders as well. Clinical trials could demonstrate the clinical benefit of this therapeutic principle in Fabry disease, mucopolysaccharidoses type I, II and VI and in Pompe disease. However, the usefulness of enzyme replacement therapy is limited due to the fact that a given enzyme preparation does not have beneficial effects on all aspects of a disorder in the same degree. Additionally, clinical studies have shown that many symptoms of a lysosomal storage disorder even after long-term treatment are no more reversible. A further novel therapeutic option for lysosomal storage disorders consists of the application of small molecules that either inhibit a key enzyme which is responsible for substrate synthesis (substrate deprivation) or act as a chaperone to increase the residual activity of the lysosomal enzyme (enzyme enhancing therapy). Various gene therapeutic techniques (in vivo and ex vivo technique) have been developed in order to administer the gene that is defective in a patient to the bloodstream or directly to the brain in order to overcome the blood-brain barrier. This review will give an insight into these newly developed therapeutic strategies and will discuss their advantages and limitations.

Evidence-based recommendations for monitoring bone disease and the response to enzyme replacement therapy in Gaucher patients

BACKGROUND

Bone disease is a serious complication of Gaucher disease. Untreated, it can result in pain, permanent bone damage and disability. Enzyme replacement therapy reverses many of the clinical signs of Gaucher bone disease but early assessment and treatment, and regular monitoring, are essential in optimising outcomes.

SCOPE

In September 2005, a group of European experts met to review current knowledge and identify best practice and unmet needs in the monitoring of Gaucher bone disease and the response to enzyme replacement therapy.

METHODS

Medline searches of peer-reviewed literature (no date restrictions) were conducted and supplemented by additional information considered relevant by panellists to furthering discussions.

FINDINGS AND CONCLUSIONS

The group's recommendations included: currently used biochemical bone markers are not clinically practical or reliable; plain X-rays should not be the sole method of assessing bone disease; MRI is the most sensitive method for monitoring bone marrow infiltration by Gaucher cells; semi-quantitative methods for assessing bone marrow infiltration in routine clinical practice should use readily available technology, include an assessment of Gaucher cell infiltration in the lumbar spine and femur, and be validated for inter-rater reliability and in comparison to other methods; a multidisciplinary approach is required for the treatment of Gaucher patients; all Gaucher patients should receive a comprehensive initial radiologic evaluation for bone disease and ongoing radiological monitoring at least once every 2 years.

Therapeutic goals in the treatment of Gaucher disease

Gaucher disease, the most common lysosomal storage disorder, is a heterogeneous multisystem condition. Patients with non-neuronopathic (type 1) Gaucher disease may suffer from hepatomegaly, splenomegaly, thrombocytopenia, bleeding tendencies, anemia, hypermetabolism, skeletal pathology, growth retardation, pulmonary disease, and decreased quality of life. Enzyme replacement therapy (ERT) with mannose-terminated glucocerebrosidase reverses or ameliorates many of the manifestations of type 1 Gaucher disease. However, the variable disease pattern and severity, and the uncertain manner of progression, render the decision to initiate ERT difficult. Thus, implementation of treatment and evaluation of the therapeutic response must be tailored to the individual patient. To obtain an evidence-based consensus on contemporary therapeutic goals, an international panel of physicians with extensive clinical experience in Gaucher disease met to review the extant literature on its treatment. The panel adopted an integrated system-based approach to arrive at a comprehensive guide to individualized management. Here we establish goals of treatment in Gaucher disease and propose a comprehensive schedule of monitoring of all relevant aspects to confirm the achievement, maintenance, and continuity of the therapeutic response.

Orthopedic considerations in Gaucher disease since the advent of enzyme replacement therapy

Gaucher disease, the most prevalent lysosomal storage disorder, is characterized by hepatosplenomegaly, hypersplenism, and rarely, neurological involvement. The most variable symptoms relate to skeletal disease, and both onset and progression are difficult to predict on the basis of genotype. This review describes findings from a large referral clinic (> 500 patients) and from the literature in the decade since the advent of specific enzyme replacement therapy. Such therapy is effective in reducing visceral and hematological involvement, but its greatest advantage as regards the skeleton is prevention of irreversible damage. Avascular necrosis of the joints-particularly the hips but also the knees and shoulders-and pathological fractures of the long bones including the ribs, as well as episodic "crises' of bone pain in children and young adults, are common manifestations. Various imaging modalities should be performed at baseline for life-long monitoring, and then as required because of specific complaints. Surgical interventions such as joint arthroplasties are important adjuvant treatments in this population; presurgical hematological profiling plus antibiotic cover and postoperative pain control are equally critical. Opportunities for orthopedic consultations with senior surgeons are not abused by our patients. These reflect disease-related morbidity, with greater numbers of requests being made by patients requiring enzyme therapy, who by definition have more severe disease characteristics.

MRI of the marrow in the paediatric skeleton

Magnetic resonance imaging (MRI) has greatly advanced evaluation of marrow diseases of the paediatric skeleton. As with many other aspects of paediatric radiology it is important to recognize the normal variations in the appearance of the marrow that occur in the growing child. These normal variations need to be differentiated from diseases and conditions that affect the marrow. This review describes the normal changes that occur in children with age, and the appearances of the pathological changes seen in infection, infiltration, haematological disorders, transplantation and radiation therapy.

Quantification of bone involvement in Gaucher disease: MR imaging bone marrow burden score as an alternative to Dixon quantitative chemical shift MR imaging--initial experience

PURPOSE

To develop a semiquantitative magnetic resonance (MR) imaging bone marrow burden (BMB) score with inclusion of both axial and peripheral bone marrow in Gaucher disease as an alternative to MR imaging with the Dixon quantitative chemical shift imaging (QCSI) technique.

MATERIALS AND METHODS

Two experienced musculoskeletal radiologists with no experience in evaluating Gaucher disease blindly analyzed MR images of lumbar spines and femora. Interobserver and intraobserver variability were tested. In addition, the BMB score was determined as a parameter to evaluate bone marrow response to enzyme supplementation therapy. Finally, the BMB score was compared with fat fraction measurements obtained with Dixon QCSI. Differences between groups were analyzed by using the nonparametric Mann-Whitney test. A P value of less than.05 was considered to represent significance. Correlation was calculated by using two-tailed nonparametric rank correlation (Spearman rho).

RESULTS

In 30 patients (mean age, 39.3 years; age range, 12-71 years) the mean fat fraction was 0.20 (range, 0.08-0.40). The BMB score range was 3-13 points. A significant correlation was found between the two observers when using BMB (rho = 0.91, P <.001). The intraobserver variation showed a significant correlation (rho = 0.99, P <.001). There was a significant correlation between BMB and QCSI (rho = -0.78, P <.001). Although BMB was less sensitive than Dixon QCSI, it showed enough sensitivity to allow detection of bone marrow response to enzyme supplementation therapy.

CONCLUSION

BMB is a reproducible semiquantitative scoring system that is easy to use. It combines MR imaging of both axial and peripheral bone marrow and shows a significant correlation with QCSI.

Imaging and quantifying skeletal involvement in Gaucher disease

Radiological imaging is used in patients with Gaucher disease to estimate the disease burden, to evaluate the presence of specific skeletal complications and to track response to therapy. MRI is currently the best technique for assessing bone marrow involvement in Gaucher disease. Gaucher cell infiltrated bone marrow is characterized by an abnormal low signal intensity on conventional T1- and T2-weighted spin echo sequences, owing to a reduction in fat marrow, which gives a high signal intensity. Enzyme replacement therapy results in a degradation of Gaucher cell deposits with a reconversion of marrow fat and consequently an increased signal on T(1)-weighted images. Conventional MRI also detects other skeletal complications in Gaucher disease, including oedema resulting from acute bone infarction, infection and trauma, avascular necrosis, pathological fractures and vertebral compression. The main drawback of conventional MRI is that it is not quantitative. Quantitative chemical shift imaging is the most sensitive quantitative method for evaluating bone marrow but is not widely available. Alternative MRI-based methods include calculation of the T1 relaxation constant and proton spectroscopy. Scoring of imaging changes detected on conventional MRI may be useful in estimating disease burden and risk of complications. Dual-energy X-ray absorptiometry (DXA) is sensitive to generalized osteopenia and changes in bone mineral density with extended enzyme replacement therapy. However, DXA is insensitive to local changes and cannot yet be used to predict fracture risk in these patients. Until the ideal quantitative technique is developed, conventional MRI will remain the best diagnostic modality for assessing skeletal complications in Gaucher disease and monitoring response to enzyme replacement therapy.

Response of Gaucher bone disease to enzyme replacement therapy

In Gaucher disease, enzyme replacement therapy usually reduces liver and spleen volumes and improves haematological abnormalities within 1 year. In contrast, skeletal manifestations of Gaucher disease are thought to respond more slowly. For example, decreased bone marrow glycolipid infiltration and increased bone mineral density have been reported to take up to 3-4 years of treatment. In this report, we present recent studies using T1- and T2-weighted MRI and quantitative chemical shift imaging that demonstrate decreases in abnormal glucocerebroside infiltration and increases in normal fat content of bone marrow within the first year of treatment. There was no obvious relationship between age, gender, splenectomy status or genotype and the response of bone marrow to therapy. Although the dose of enzyme replacement therapy may be related to bone marrow response, no significant relationship was demonstrated in this report. Long-term enzyme replacement therapy induces continued degradation of Gaucher cell deposits, reconversion of fat marrow and increased bone mineral density. This treatment is also associated with improved or non-progressive bone symptoms and functional status in most adult patients, and it prevents the new occurrence of bone pain and bone crisis in nearly all patients. The development of more sensitive, quantitative imaging methods will help to evaluate disease severity better and to assess the response to therapy.