Abnormal cobalamin-dependent transmethylation in AIDS-associated myelopathy

Neuropathogenesis of HIV and emerging therapeutic targets

INTRODUCTION

HIV infection causes a wide range of neurological complications, many of which are among the most common complications of chronic HIV infection in the era of combined antiretroviral therapy. These neurological conditions arise due to complex interactions between HIV viral proteins and neuronal and glial cells that lead to the activation of various inflammatory and neurotoxic pathways across the nervous system.

AREAS COVERED

This review summarizes the current literature on the pathogenesis and clinical manifestations of neurological injuries associated with HIV in the brain, spinal cord, and peripheral nervous system. Molecular pathways relevant for possible therapeutic targets or advancements are emphasized. Gaps in knowledge and current challenges in therapeutic design are also discussed.

EXPERT OPINION

Several challenges exist in the development of therapeutic targets for HIV-associated cognitive impairments. However, recent developments in drug delivery systems and treatment strategies are encouraging. Treatments for HIV-associated pain and peripheral sensory neuropathies currently consist of symptomatic management, but a greater understanding of their pathogenesis can lead to the development of targeted molecular therapies and disease-modifying therapies. HIV-associated autonomic dysfunction may affect the course of systemic disease via disrupted neuro-immune interactions; however, more research is needed to facilitate our understanding of how these processes present clinically.

Review of the neurological aspects of HIV infection

There are almost 40 million people in the world who live with the human immunodeficiency virus (HIV). The neurological manifestations associated with HIV contribute to significant morbidity and mortality despite the advances made with anti-retroviral therapy (ART). This review presents an approach to classification of neurological disorders in HIV, differentiating diseases due to the virus itself and those due to opportunistic infection. The effects of antiretroviral therapy are also discussed. The emphasis is on the developing world where advanced complications of HIV itself and infections such as tuberculosis (TB), toxoplasmosis and cryptococcal meningitis remain prevalent.

HIV infection, seasonality and younger age predicting incident Bell's palsy among black South Africans

Background

Although South Africa (SA) is facing a high prevalence of HIV infection, there is no literature from this region on a link between Bell’s palsy and HIV. The aim of this study was to identify the occurrence of Bell’s palsy in relation to demographics, seasons and HIV status among black South Africans.

Methods

This retrospective cohort was conducted among adult black patients, without Bell’s palsy in 2003, presenting to the neurology outpatients department at Dr. George Mukhari Academic hospital, Pretoria, South Africa, between 2004 (study baseline) and 2012 (end test). Gender, age, HIV status, and seasons were potential predictors of Bell’s palsy using Cox regression model and Kaplan Meier curves.

Results

From the baseline of 1487 patients, 20.9% (n = 311) experienced Bell’s palsy onset by the end of the study. In univariate analysis, male gender (RR = 2.1 95% CI 1.7–2.5; P <  0.0001), age less than 30 years (RR = 2.9 95% CI 2.4–3.6; P <  0.0001), HIV seropositivity (RR =2.9 95% CI 2.3–4.9; P < 0.0001).

The highest incidence in winter (30.3% n = 136/450) vs. incidences during other seasons with Intermediate values during Summer (25.3% n = 136/450) and Autumn (20.7% n = 64/308) and the lowest incidence in Spring (23.7% n = 16/353) P < 0.0001) were predictors of Bell’s palsy. In multivariate analysis at adjusting for gender, the most significant and independent predictors of incident Bell’s palsy were HIV seropositivity (HR = 6.3 95% CI 4.8–8.3; P < 0.0001), winter (HR = 1.6 95% CI 1.2–2.1; P < 0.0001) vs. other seasons, and younger age < 30 years (HR = 7.1 95% CI 5.6–9.1; P < 0.0001) vs. older age groups.

Conclusion

Seasonality, younger age and HIV positivity are important and independent risk factors of Bell’s palsy. Education and awareness programs on the possible effects of HIV and seasons on the development of Bell’s palsy are necessary. This would lead to a better understanding and even a possible development of avoidance measures for this condition amongst young black South Africans.

Spinal cord involvement in adult-onset metabolic and genetic diseases

In adulthood, spinal cord MRI abnormalities such as T2-weighted hyperintensities and atrophy are commonly associated with a large variety of causes (inflammation, infections, neoplasms, vascular and spondylotic diseases). Occasionally, they can be due to rare metabolic or genetic diseases, in which the spinal cord involvement can be a prominent or even predominant feature, or a secondary one. This review focuses on these rare diseases and associated spinal cord abnormalities, which can provide important but over-ridden clues for the diagnosis. The review was based on a PubMed search (search terms: 'spinal cord' AND 'leukoencephalopathy' OR 'leukodystrophy'; 'spinal cord' AND 'vitamin'), further integrated according to the authors' personal experience and knowledge. The genetic and metabolic diseases of adulthood causing spinal cord signal alterations were identified and classified into four groups: (1) leukodystrophies; (2) deficiency-related metabolic diseases; (3) genetic and acquired toxic/metabolic causes; and (4) mitochondrial diseases. A number of genetic and metabolic diseases of adulthood causing spinal cord atrophy without signal alterations were also identified. Finally, a classification based on spinal MRI findings is presented, as well as indications about the diagnostic work-up and differential diagnosis. Some of these diseases are potentially treatable (especially if promptly recognised), while others are inherited as autosomal dominant trait. Therefore, a timely diagnosis is needed for a timely therapy and genetic counselling. In addition, spinal cord may be the main site of pathology in many of these diseases, suggesting a tempting role for spinal cord abnormalities as surrogate MRI biomarkers.

HIV and spinal cord disease

The epidemiology of spinal cord disease in human immunodeficiency virus (HIV) infection is largely unknown due to a paucity of data since combination antiretroviral therapy (cART). HIV mediates spinal cord injury indirectly, by immune modulation, degeneration, or associated infections and neoplasms. The pathologies vary and range from cytotoxic necrosis to demyelination and vasculitis. Control of HIV determines the differential for all neurologic presentations in infected individuals. Primary HIV-associated acute transverse myelitis, an acute inflammatory condition with pathologic similarities to HIV encephalitis, arises in early infection and at seroconversion. In contrast, HIV vacuolar myelopathy and opportunistic infections predominate in uncontrolled disease. There is systemic immune dysregulation as early as primary infection due to initial depletion of gut-associated lymphoid tissue CD4 cells and allowance of microbial translocation across the gut that never fully recovers throughout the course of HIV infection, regardless of how well controlled. The subsequent proinflammatory state may contribute to spinal cord diseases observed even after cART initiation. This chapter will highlight an array of spinal cord pathologies classified by stage of HIV infection and immune status.

HIV neuropathology

Primary human immunodeficiency virus (HIV) neuropathologies can affect all levels of the neuraxis and occur in all stages of natural history disease. Some, like HIV encephalitis, HIV myelitis, and diffuse infiltrative lymphocytosis of peripheral nerve, reflect productive infection of the nervous system; others, like vacuolar myelopathy, distal symmetric polyneuropathy, and central and peripheral nervous system demyelination, are not clearly related to regional viral replication, and reflect more complex cascades of dysregulated host immunity and metabolic dysfunction. In pediatric patients, the spectrum of neuropathology is altered by the impacts of HIV on a developing nervous system, with microcephaly, abundant brain mineralization, and corticospinal tract degeneration as examples of this unique interaction. With efficacious therapies, CD8 T-cell encephalitis is emerging as a significant entity; often this is clinically recognized as immune reconstitution inflammatory syndrome, but has also been described in the context of viral escape and treatment interruption. The relationship of HIV neuropathology to clinical symptoms is sometimes straightforward, and sometimes mysterious, as individuals can manifest significant deficits in the absence of discrete lesions. However, at all stages of the natural history disease, neuroinflammation is abundant, and critical to the generation of clinical abnormality. Neuropathologic and neurobiologic investigations will be central to understanding HIV nervous system disorders in the era of efficacious therapies.

Advances in clinical determinants and neurological manifestations of B vitamin deficiency in adults

B vitamin deficiency is a leading cause of neurological impairment and disability throughout the world. Multiple B vitamin deficiencies often coexist, and thus an understanding of the complex relationships between the different biochemical pathways regulated in the brain by these vitamins may facilitate prompter diagnosis and improved treatment. Particular populations at risk for multiple B vitamin deficiencies include the elderly, people with alcoholism, patients with heart failure, patients with recent obesity surgery, and vegetarians/vegans. Recently, new clinical settings that predispose individuals to B vitamin deficiency have been highlighted. Moreover, other data indicate a possible pathogenetic role of subclinical chronic B vitamin deficiency in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. In light of these findings, this review examines the clinical manifestations of B vitamin deficiency and the effect of B vitamin deficiency on the adult nervous system. The interrelationships of multiple B vitamin deficiencies are emphasized, along with the clinical phenotypes related to B vitamin deficiencies. Recent advances in the clinical determinants and diagnostic clues of B vitamin deficiency, as well as the suggested therapies for B vitamin disorders, are described.

Neurologic aspects of cobalamin (B12) deficiency

Optimal functioning of the central and peripheral nervous system is dependent on a constant supply of appropriate nutrients. Particularly important for optimal functioning of the nervous system is cobalamin (vitamin B12). Cobalamin deficiency is particularly common in the elderly and after gastric surgery. Many patients with clinically expressed cobalamin deficiency have intrinsic factor-related malabsorption such as that seen in pernicious anemia. The commonly recognized neurological manifestations of cobalamin deficiency include a myelopathy with or without an associated neuropathy. This review deals with neurological aspects of vitamin B12 deficiency and attempts to highlight recent developments.

Nuclear magnetic resonance based profiling of biofluids reveals metabolic dysregulation in HIV-infected persons and those on anti-retroviral therapy

BACKGROUND

Although HIV causes immune deficiency by infection and depletion of immunocytes, metabolic alterations with clinical manifestations are also reported in HIV/AIDS patients. Here we aimed to profile metabolite changes in the plasma, urine, and saliva of HIV/AIDS patients, including those on anti-retroviral therapy (ART).

METHODS

Metabolic profiling of biofluids collected from treatment naïve HIV/AIDS patients and those receiving ART was done with solution-state nuclear magnetic resonance (NMR) spectroscopy followed by statistical analysis and annotation.

RESULTS

In Principal Component Analysis (PCA) of the NMR spectra, Principal Component 1 (PC1) alone accounted for 99.3%, 87.2% and 78.8% variations in plasma, urine, and saliva, respectively. Partial least squares discriminant analysis (PLS-DA) was applied to generate three-component models, which showed plasma and urine to be better than saliva in discriminating between patients and healthy controls, and between ART-naïve patients and those receiving therapy. Twenty-six metabolites were differentially altered in any or two types of samples. Our results suggest that urinary Neopterin, and plasma Choline and Sarcosine could be used as metabolic biomarkers of HIV/AIDS infection. Pathway analysis revealed significant alternations in 12 metabolic pathways.

CONCLUSIONS

This study catalogs differentially regulated metabolites in biofluids, which helped classify subjects as healthy controls, HIV/AIDS patients, and those on ART. It also underscores the importance of further studying the consequences of HIV infection on host metabolism and its implications for pathogenesis.

Nutritional disorders in tropical neurology

About three-fourths of the total world population live in the tropics but consume only 6% of worldwide food production and contribute 15% of the world's net revenue explaining the short life expectancy, high infantile mortality, and poor daily caloric intake; moreover, lack of clean drinking water and deficient sanitation promote water-borne infections, diarrhea, and risk of malabsorption that contribute to the prevalence of malnutrition in the tropics. One-third of the world's population consumes insufficient iodine increasing the risk for mental retardation and deafness due to maternal hypothyroidism. The main nutritional syndromes comprise protein-energy malnutrition (marasmus and kwashiorkor); nutritional neuropathies, myelopathies and neuromyelopathies, as well as specific deficiencies of vitamins and micronutrients including iodine, iron, zinc, and selenium.

Cobalamin C defect: natural history, pathophysiology, and treatment

Cobalamin C (Cbl-C) defect is the most common inborn cobalamin metabolism error; it causes impaired conversion of dietary vitamin B12 into its two metabolically active forms, methylcobalamin and adenosylcobalamin. Cbl-C defect causes the accumulation of methylmalonic acid and homocysteine and decreased methionine synthesis. The gene responsible for the Cbl-C defect has been recently identified, and more than 40 mutations have been reported. MMACHC gene is located on chromosome 1p and catalyzes the reductive decyanation of CNCbl. Cbl-C patients present with a heterogeneous clinical picture and, based on their age at onset, can be categorized into two distinct clinical forms. Early-onset patients, presenting symptoms within the first year, show a multisystem disease with severe neurological, ocular, haematological, renal, gastrointestinal, cardiac, and pulmonary manifestations. Late-onset patients present a milder clinical phenotype with acute or slowly progressive neurological symptoms and behavioral disturbances. To improve clinical course and metabolic abnormalities, treatment of Cbl-C defect usually consists of a combined approach that utilizes vitamin B12 to increase intracellular cobalamin and to maximize deficient enzyme activities, betaine to provide a substrate for the conversion of homocysteine into methionine through betaine-homocysteine methyltransferase, and folic acid to enhance remethylation pathway. No proven efficacy has been demonstrated for carnitine and dietary protein restriction. Despite these measures, the long-term follow-up is unsatisfactory especially in patients with early onset, with frequent progression of neurological and ocular impairment. The unfavorable outcome suggests that better understanding of the pathophysiology of the disease is needed to improve treatment protocols and to develop new therapeutic approaches.

Diffusion tensor MR imaging (DTI) metrics in the cervical spinal cord in asymptomatic HIV-positive patients

INTRODUCTION

This study was conducted to compare diffusion tensor MR imaging (DTI) metrics of the cervical spinal cord in asymptomatic human immunodeficiency virus (HIV)-positive patients with those measured in healthy volunteers, and to assess whether DTI is a valuable diagnostic tool in the early detection of HIV-associated myelopathy (HIVM).

METHODS

MR imaging of the cervical spinal cord was performed in 20 asymptomatic HIV-positive patients and in 20 healthy volunteers on a 3-T MR scanner. Average fractional anisotropy (FA), mean diffusivity (MD), and major (E1) and minor (E2, E3) eigenvalues were calculated within regions of interest (ROIs) at the C2/3 level (central and bilateral anterior, lateral and posterior white matter).

RESULTS

Statistical analysis showed significant differences with regard to mean E3 values between patients and controls (p = 0.045; mixed-model analysis of variance (ANOVA) test). Mean FA was lower, and mean MD, mean E1, and mean E2 were higher in each measured ROI in patients compared to controls, but these differences were not statistically significant.

CONCLUSION

Asymptomatic HIV-positive patients demonstrate only subtle changes in DTI metrics measured in the cervical spinal cord compared to healthy volunteers that currently do not support using DTI as a diagnostic tool for the early detection of HIVM.

Neurologic presentations of AIDS

The human immunodeficiency virus (HIV), the cause of AIDS, has infected an estimated 33 million individuals worldwide. HIV is associated with immunodeficiency, neoplasia, and neurologic disease. The continuing evolution of the HIV epidemic has spurred an intense interest in a hitherto neglected area of medicine, neuroinfectious diseases and their consequences. This work has broad applications for the study of central nervous system (CNS) tumors, dementias, neuropathies, and CNS disease in other immunosuppressed individuals. HIV is neuroinvasive (can enter the CNS), neurotrophic (can live in neural tissues), and neurovirulent (causes disease of the nervous system). This article reviews the HIV-associated neurologic syndromes, which can be classified as primary HIV neurologic disease (in which HIV is both necessary and sufficient to cause the illness), secondary or opportunistic neurologic disease (in which HIV interacts with other pathogens, resulting in opportunistic infections and tumors), and treatment-related neurologic disease (such as immune reconstitution inflammatory syndrome).

Neurologic presentations of nutritional deficiencies

Optimal functioning of the central and peripheral nervous system is dependent on a constant supply of appropriate nutrients. The first section of this review discusses neurologic manifestations related to deficiency of key nutrients such as vitamin B(12), folate, copper, vitamin E, thiamine, and others. The second section addresses neurologic complications related to bariatric surgery. The third sections includes neurologic presentations caused by nutrient deficiencies in the setting of alcoholism. The concluding section addresses neurologic deficiency diseases that have a geographic predilection.

Elevated levels of vitamin B12 and folate in vertically infected children with HIV-1

OBJECTIVE

Neurologic and hematologic abnormalities are common in HIV-infected children and may be related to concomitant deficiencies in serum B12 and folate, which are highly prevalent in HIV-infected adults. We sought to determine the prevalence of B12 and folate deficiencies in HIV-infected children in the United States.

METHODS

Cross-sectional information on demographics, folate and B12 levels, hematological parameters, concurrent CD4%, HIV-viral load and antiretroviral regimens were abstracted from the medical records of 103 vertically infected children followed in an outpatient pediatric HIV clinic in the Bronx, during 2001-2002.

RESULTS

Mean age was 10 years (+/-4.4 years), 46% were male, 53% African-American and 46% Hispanic. Nineteen percent had significant immunologic suppression and 18 children had AIDS. All were receiving combination antiretroviral therapy and 66% were on a protease inhibitor-based regimen. Sixteen were taking cotrimoxazole prophylaxis. None were taking multivitamins or manifested clinical evidence of gastrointestinal malabsorption. All patients had serum folate or B12 levels within or above the normal range. Children with elevated B12 were significantly more likely to be younger (P = 0.0002) and have higher mean folate levels (P = 0.0004) compared with children with normal serum B12. In a multivariate logistic regression analysis, factors independently associated with elevated levels of vitamin B12 included: elevated serum folate [odds ratio (OR): 3.2; P = 0.01], nonnucleoside reverse transcriptase inhibitor use (OR: 0.38; P = 0.05) and female sex (OR: 0.67; P = 0.42)

CONCLUSION

Folate and B12 deficiencies are uncommon in HIV-infected children in the United States, suggesting that routine supplementation with B12 and folate is not indicated without confirmation of micronutrient deficiency.

Progressive vacuolar myelopathy and leukoencephalopathy in childhood acute lymphoblastic leukemia and transient improvement with vitamin B12

Vacuolar myelopathy (VM) in leukemia is rare. We report a boy with leukemia who developed isolated central nervous system (CNS) relapse during reinduction therapy. 5 months after cranial radiotherapy, he gradually developed quadriparesis. Magnetic resonance imaging revealed an intramedullary lesion which extended through the cervical spine. Serum vitamin B12, folic acid, cerebrospinal fluid methyl malonic acid were normal. Viral screening by ELISA was negative. He had lymphopenia, and reduced immunoglobulins, from a cardiac arrest. Biopsy revealed VM. He responded to weekly vitamin B12 treatment but on the 6th week of the therapy he died after developing periventricular, gliotic, hyperintense lesions in the brain.

Demyelinating and infectious diseases of the spinal cord

Spinal cord diseases generally have distinctive clinical findings that reflect dysfunction of particular sensory or motor tracts. The abnormalities on MR images reflect the pathologic changes that occur in the affected pathways. The complexity and the wide spectrum of diseases affecting the spinal cord require a profound knowledge of neuropathology and exactly tuned imaging strategies. This article describes and illustrates the clinical and imaging characteristics in various demyelinating and infectious conditions of the spinal cord.

Nutritional neuropathies

Optimal functioning of the central and peripheral nervous system is dependent on appropriate nutrients. Neurologic consequences of nutritional deficiencies are not restricted to underdeveloped countries. Multiple nutritional deficiencies can coexist. Obesity is of particular concern in the developed world. The rising rate of bariatric surgery are accompanied by neurologic complications related to nutrient deficiencies. Prognosis depends on prompt recognition and institution of appropriate therapy. This review discusses peripheral nervous system manifestations related to the deficiency of key nutrients, neurologic complications associated with bariatric surgery, and conditions that have a geographic significance associated with bariatric surgery and certain conditions that have a geographic predilection.

Viral myelitis: An update

Viral infections of the central nervous system are uncommon but are important in the differential diagnosis of acute myelopathy. Acute viral myelitis can present as acute flaccid paralysis (poliomyelitis) or neurologic dysfunction due to involvement of the white matter. The latter usually affects only part of the transverse expanse of the spinal cord and manifests as asymmetric motor and sensory symptoms. When both halves of the spinal cord are affected, the entity is referred to as acute transverse myelitis and patients exhibit uniformly symmetric weakness, sensory loss, and urinary bladder involvement. Acute flaccid paralysis is due to cytolytic infection of anterior horn cells. When the involvement is mainly white matter, virus-specific and autoimmune host cellular immune responses are believed to contribute to spinal cord damage. Acute flaccid paralysis is caused by polioviruses-1, -2, and -3; coxsackieviruses A and B; enterovirus-71; and flaviviruses, including West Nile virus. Involvement of spinal cord white matter may be associated with infection by many different viruses; however, in most cases a specific viral cause is never determined. Chronic myelitis may be due to either direct infection of the spinal cord by human T-cell lymphotrophic virus-1 (HTLV-1), or a metabolic disturbance due to HIV-1 infection in AIDS patients; no other human virus is known to chronically infect the spinal cord without involvement of the brain. The principal treatment is antiviral drugs immediately upon virus isolation or the identification of a viral sequence by PCR and, when indicated, high doses of methylprednisolone.

Imaging of neuro-AIDS

The pathogenesis of the human immunodeficiency virus (HIV) infection of the central nervous system and the imaging presentation of patients with neurological complications from HIV/AIDS are discussed. Imaging findings are often nonspecific; however, correlations with patient's clinical signs and CD4 count allow a working diagnosis to be made.

Atteintes du système nerveux central et infection par le VIH-1

Central nervous system complications are common in HIV-1 infected patients and occur either as a result of concomitant immunosuppression (opportunistic infections, lymphoma and tumors), as a primary manifestation of HIV infection, or as an adverse effect of therapy (immune restoration and toxicity). These complications contribute largely to patient morbidity and mortality. In the era of highly active antiretroviral therapy (HAART) these disease states have changed in presentation, outcome and incidence. We review in detail the epidemiology, pathogenesis, clinical features, diagnosis, and management of these disorders.

Nitrous oxide inhalation as a cause of cervical myelopathy

Current evidence suggests that the incidence of recreational nitrous oxide inhalation is on the rise. Due to the possibility of clinically significant myelopathy, as well as potential response to treatment, it is important to consider this diagnosis when appropriate. We present a case of acquired ataxia and myelopathy due to nitrous oxide abuse and discuss diagnosis, pathophysiology, and response to treatment.

Neurological complications of HIV infection

Cognitive disorders, vacuolar myelopathy, and sensory neuropathies associated with HIV are the most common disorders in patients with HIV AIDS, and are the focus of this review. These disorders are treatable and of those associated with HIV AIDS the pathogenic mechanisms are the most understood. Although triggered by productive HIV macrophage infections, aberrant immune activation plays a major role in inducing the CNS disorders. Novel therapies aimed at these inflammatory mechanisms can be effective. The sensory neuropathies associated with HIV infection are a major cause of morbidity; incidence may be increased by the toxic effects of specific antiretroviral drugs within the peripheral nervous system.

Cobalamin (vitamin B12) in subacute combined degeneration and beyond: traditional interpretations and novel theories

Subacute combined degeneration (SCD) is a neuropathy due to cobalamin (Cbl) (vitamin B(12)) deficiency acquired in adult age. Hitherto, the theories advanced to explain the pathogenesis of SCD have postulated a causal relationship between SCD lesions and the impairment of either or both of two Cbl-dependent reactions. We have identified a new experimental model, the totally gastrectomized rat, to reproduce the key morphological features of the disease [spongy vacuolation, intramyelinic and interstitial edema of the white matter of the central nervous system (CNS), and astrogliosis], and found new mechanisms responsible for the pathogenesis of SCD: the neuropathological lesions in TGX rats are not only due to mere vitamin withdrawal but also to the overproduction of the myelinolytic tumor necrosis factor (TNF)-alpha and the reduced synthesis of the two neurotrophic agents, epidermal growth factor (EGF) and interleukin-6. This deregulation of the balance between TNF-alpha and EGF synthesis induced by Cbl deficiency has been verified in the sera of patients with pernicious anemia (but not in those with iron-deficient anemia), and in the cerebrospinal fluid (CSF) of SCD patients. These new functions are not linked to the coenzyme functions of the vitamin, but it is still unknown whether they involve genetic or epigenetic mechanisms. Low Cbl levels have also been repeatedly observed in the sera and/or CSF of patients with Alzheimer's disease or multiple sclerosis, but whether Cbl deficit plays a role in the pathogenesis of these diseases is still unclear.

Cobalamin-responsive disorders in the ambulatory care setting: unreliability of cobalamin, methylmalonic acid, and homocysteine testing

Early recognition of cobalamin (Cbl)-responsive disorders in the ambulatory care setting is essential to prevent irreversible neurologic deficits. However, diagnostic algorithms using Cbl, methylmalonic acid (MMA), and homocysteine (HCys) measurements reflect studies in academic centers, and their negative predictive values have not been established. Thus, records of 456 ambulatory patients evaluated for Cbl deficiency at a staff model HMO were reviewed. Pretherapy Cbl, MMA, and HCys values in individual patients varied by 23%, 23%, and 17%, respectively, over 2 to 6 weeks. Hematologic or neurologic responses to pharmacologic doses of Cbl occurred in 37 of the 95 evaluable patients. In these patients, pretherapy Cbl, MMA, and HCys values were normal in 54%, 23%, and 50%, respectively. If therapy had been restricted to symptomatic patients with both low or intermediate Cbl levels and increased metabolite values, 63% of responders would not have been treated. Twenty-five patients did not respond to treatment, including 5 of 11 patients (45%) with low Cbl, 22 of 49 patients (45%) with high MMA, and 13 of 30 patients (43%) with high HCys values. It is concluded that Cbl, MMA, and HCys levels fluctuate with time and neither predict nor preclude the presence of Cbl-responsive hematologic or neurologic disorders.

Degenerative myelopathy associated with cobalamin deficiency in a cat

A severe myelopathy was observed in a 9-year-old neutered male cat with a clinical history of chronic pancreatitis associated with deficiency of serum cobalamin and folates concentrations, and progressive spinal ataxia. The spinal cord lesions mainly involved the dorsal columns of the caudal cervical and cervico-thoracic segments, and were characterized by diffuse vacuolated myelin sheaths and axonal degeneration, marked gliosis, fibrosis and presence of gitter cells. The pancreas showed severe atrophy of the exocrine tissue, periductular fibrosis and infiltration of inflammatory cells, consistent with chronic interstitial pancreatitis. This condition can be accountable for cobalamin deficiency, as the pancreas is the only source of intrinsic factor in cats. The spinal cord lesions in the cat of this report resembled the subacute combined degeneration of the spinal cord described in human beings with cobalamin deficiency and hence a similar pathogenetic mechanism is hypothesized.