Muscle Dystrophy Differential Diagnosis: Manifestation of Anti-HMG-CoA Reductase Antibody Myositis in Infancy

Background: Inflammatory myopathies in childhood are either transient following viral infection or chronic-like dermatomyositis. We report a 13-year-old girl with a recently described form of chronic myositis.

Case Report: The early motor development of the patient was normal. By the age of 4 years, she developed generalized muscular weakness and toe walking. By the age of 6 years, she needed a wheelchair for longer distances. On the skin she had few erythematous papulae diagnosed as prurigo simplex acuta. At that time CK was 9,800 U/L. A muscle biopsy performed at the age of 5 years showed a necrotizing myopathy without signs of myositis. In process of the following years, the weakness was fluctuating but slowly progressive. Genetic analyses for hereditary myopathies were inconclusive. A muscle MRI showed no specific results.

Results: Analysis of anti-HMG-CoA reductase (HMGCR) antibodies showed extremely elevated levels with 352 U/mL (normal < 20). The patient had never been treated with HMGCR inhibitors. Antibodies typical for other kinds of myositis were not found.

Conclusion: Toxic myopathies and rhabdomyolysis due to a treatment with HMGCR inhibitors are well-known side effects of these substances. Liang et al (2016) recently described a HMGCR antibody myositis in 9 of 62 pediatric patients with myopathies of unknown origin and without previous statin therapy. The youngest patient was 10 months old. Two children showed fluctuating populous skin alterations. In our patient, the finding of anti-HMGCR antibodies leads to the clarification of a case of a presumed genetic myopathy. The analysis of HMGCR antibodies should be considered early in the differential diagnosis of unclear myopathies.