Amyopathic Dermatomyositis in Children: A Diagnostic and Therapeutic Dilemma

MDA5 autoantibody-another indicator of clinical diversity in dermatomyositis

Allenbach and colleagues have recently reported for the first time the results of an intriguing study of the histopathologic, immunopathologic and gene expression differences in muscle biopsy tissue from adult dermatomyositis (DM) patients who do and do not have circulating MDA5 autoantibodies (anti-MDA5). Anti-MDA5 were originally identified in a clinically-defined subset of DM patients whose disease was expressed predominately in the skin for unusually long periods of time without accompanying muscle weakness [i.e., "clinically-amyopathic DM" (CADM)] and were at risk for acute, rapidly-progressive form of interstitial lung disease (ILD). As an academic dermatologist in the United States of America (USA) having a career-long interest in the CADM subset, I would like to share my perspective on the results of the work by Allenbach and colleagues and offer some suggestions for additional study in this area. But to do so most effectively, I first would like to review the clinical concept of CADM and its association with anti-MDA5 antibody production and a potentially-fatal form of (ILD).

The juvenile idiopathic inflammatory myopathies: pathogenesis, clinical and autoantibody phenotypes, and outcomes

The aim of this review was to summarize recent advances in the understanding of the clinical and autoantibody phenotypes, their associated outcomes and the pathogenesis of the juvenile idiopathic inflammatory myopathies (JIIMs). The major clinical and autoantibody phenotypes in children have many features similar to those in adults, and each has distinct demographic and clinical features and associated outcomes. The most common myositis autoantibodies in JIIM patients are anti-p155/140, anti-MJ and anti-MDA5. Higher mortality has been associated with overlap myositis as well as with the presence of anti-synthetase and anti-MDA5 autoantibodies; a chronic illness course and lipodystrophy have been associated with anti-p155/140 autoantibodies; and calcinosis has been associated with anti-MJ autoantibodies. Histologic abnormalities of JIIMs detectable on muscle biopsy have also been correlated with myositis-specific autoantibodies; for example, patients with anti-MDA5 show low levels of inflammatory infiltrate and muscle damage on biopsy. The first genome-wide association study of adult and juvenile dermatomyositis revealed three novel genetic associations, BLK, PLCL1 and CCL21 and confirmed that the human leucocyte antigen region is the primary risk region for juvenile dermatomyositis. Here, we review the well-established pathogenic processes in JIIMs, including the type 1 interferon and endoplasmic reticulum stress pathways. Several novel JIIM-associated inflammatory mediators, such as the innate immune system proteins, myeloid-related peptide 8/14, galectin 9 and eotaxin, have emerged as promising biomarkers of disease. Advances in our understanding of the phenotypes and pathophysiology of the JIIMs are leading to better tools to help clinicians stratify and treat these heterogeneous disorders.

Developments in the classification and treatment of the juvenile idiopathic inflammatory myopathies

This review updates recent trends in the classification of the juvenile idiopathic inflammatory myopathies (JIIM) and the emerging standard of treatment of the most common form of JIIM, juvenile dermatomyositis. The JIIM are rare, heterogeneous autoimmune diseases that share chronic muscle inflammation and weakness. A growing spectrum of clinicopathologic groups and serologic phenotypes defined by the presence of myositis autoantibodies are now recognized, each with differing demographics, clinical manifestations, laboratory findings, and prognoses. Although daily oral corticosteroids remain the backbone of treatment, disease-modifying anti-rheumatic drugs are almost always used adjunctively and biologic therapies may benefit patients with recalcitrant disease.

Is juvenile dermatomyositis a different disease in children up to three years of age at onset than in children above three years at onset? A retrospective review of 23 years of a single center's experience

BACKGROUND

We tested the hypothesis that the course and outcome of juvenile dermatomyositis (JDM) in children seen at one center with the JDM disease onset at or below three years of age is different from that in the children with disease onset at greater than three years of age.

METHODS

Institutional Review Board approval was obtained to retrospectively review the charts of 78 patients from age 0-18 years with JDM seen in the pediatric rheumatology clinic at Nationwide Children's Hospital in Columbus, Ohio over the past 23 years from January 1988. The diagnosis was made by the treating pediatric rheumatologist. Not all the patients met the Bohan and Peter criteria, as muscle biopsy and EMG were not always performed and we utilized a modified JDM criteria. The data regarding disease course and outcome were collected as of the last clinic follow-up or to July 1, 2010. We used the Wilcoxon Two-Sample test to compare numerical variables between two age groups, and used logistic regression to compare categorical variables between two age groups in SAS 9.1.3. Minitab-16 was used to calculate various mean, median, modes, standard deviations and range. For survival analysis, we used Kaplan-Meier method with log-rank test.

RESULTS

The mean age of onset in the two groups at Nationwide Children's Hospital was 27 months and 91 months. The mean times between onset of symptoms to diagnosis in the younger and older age groups was 5.6 months and 4.5 months, respectively, not a statistically significant difference. The younger onset group had more females (p=0.05) and their disease onset occurred less frequently during the typical winter-spring seasons (p=0.031). The younger onset group was more likely to have a preceding fever (p=0.029) and family history of autoimmune diseases (p=0.012). The younger onset group was less likely to have heliotrope rash (p=0.04), Gottron's sign (p=0.049), capillary loop abnormalities (p=0.010), or elevations in creatine kinase (CK, p=0.022), aspartate aminotransferase (AST, p=0.021) or aldolase (p=0.035). The younger onset group was treated less often with pulse methylprednisolone at diagnosis (p=0.043) and less often with hydroxychloroquine (p=0.035). There were no differences between the two groups regarding initial oral steroid dose (p=0.8017), number of patients who received methotrexate at diagnosis (p=0.709), and the number who ever received other immunosuppressants (p=0.323). The mean and maximum duration (mean duration 24.3 months vs. 35.2 months, maximum duration 51 vs. 124 months in younger and older onset group respectively) of methotrexate therapy, and the mean and maximum duration of oral steroid therapy (Mean duration 16.8 months vs. 33.3 months, maximum duration 50 vs. 151 months in younger and older onset group respectively), was shorter in the younger group. The younger onset patients were less likely to have active disease at 5 years (9% vs. 35.7%, p=0.015) and 10 years post-diagnosis (9% vs. 45.1%, p=0.011, Table 7). The younger patients were less likely to have osteonecrosis (p=0.023). Two disease-related deaths occurred in the younger group, none in the older group. The results of the survival analysis showed that the difference between the age groups was statistically significant (p < 0.012). The sex and race were not significant (p> 0.26 and p>0.95, respectively).

CONCLUSIONS

There were significant differences between JDM patients with disease onset at or below age three years at our center, compared to their older counterparts. Younger patients in our cohort had fewer typical findings at diagnosis and a milder disease course without needing as long a duration of corticosteroids and immunosuppression. Patients with a younger onset had a higher mortality rate but mortalities were unusual and numbers small. The younger group had a similar complication rate compared to the older onset patients, except for osteonecrosis which was higher in the older onset group. These findings differ from the previous reports that a younger age of onset in JDM is often associated with a more severe disease, as results at our center suggest that children with younger onset JDM appear to be atypical but may do well compared to the older JDM patients.

A systematic review of juvenile-onset clinically amyopathic dermatomyositis

BACKGROUND

Dermatomyositis (DM) presenting during childhood or adolescence classically encompasses hallmark cutaneous changes, proximal muscle weakness, and laboratory evidence of myositis. When cutaneous manifestations of DM are present without muscle weakness for > 6 months, the term 'clinically amyopathic DM' applies (syn. DM sine myositis).

OBJECTIVES

To review the clinical and epidemiological features of published cases of juvenile-onset clinically amyopathic DM, with comparison with adult-onset clinically amyopathic DM and juvenile-onset classical DM.

METHODS

Systematic review of the published literature.

RESULTS

We identified 68 cases of juvenile-onset clinically amyopathic DM published during 1963-2006. The disease in 18 of 68 (26%) patients subsequently evolved to classical DM. Overall, the mean age at diagnosis was 10.8 years (range 2-17) with nearly equal male/female ratio and mean follow-up of 3.9 years. Among cases with diagnostic testing, 10 of 19 had a positive antinuclear antibody titre, two of nine had elevated erythrocyte sedimentation rate and two of 51 had elevated creatine kinase (CK). Of patients with normal CK, three of 22 had abnormal electromyography, one of 19 had abnormal muscle biopsy, and one of nine had abnormal magnetic resonance imaging. Calcinosis was reported in three of 68. No cases of severe vasculopathy (resulting in ulceration), interstitial lung disease or internal malignancy were reported.

CONCLUSIONS

This review suggests a good prognosis for children with clinically amyopathic DM. A minority of patients with negative muscle enzymes had positive ancillary testing for myositis, and these patients rarely developed muscle weakness. Predictive factors for progression to classical DM were not identified. Symptomatic treatment of cutaneous involvement and close clinical monitoring may be an alternative to aggressive immunosuppression.

Drug-Induced Amyopathic Dermatomyositis

Amyopathic dermatomyositis is a rare condition. We describe the clinical and histopathologic findings of a 53-year-old woman who developed cutaneous lesions similar to those described in dermatomyositis after fibrate therapy for hypertriglyceridemia. Our patient fits the proposed criteria for amyopathic dermatomyositis, and after 8.5 years, muscular involvement has not been detected, although the dermatologic lesions are still present despite different treatments reported to treat this condition (steroids, antimalarials, methotrexate, dapsone). However, an initial good response has been observed with thalidomide, a drug used increasingly in the dermatologic field. As far as we know, this case is the first of drug-induced amyopathic dermatomyositis.