A Child with Refractory and Relapsing Anti-3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase Myopathy
What is it about?
Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR) myopathy is usually characterized by progressive proximal muscle weakness prominent in the lower extremities, with the elevation of creatine kinase (CK). Since it is a very rare disease and the number of reported pediatric cases is low, there is no clear consensus on its management. Here, we present a pediatric patient with anti-HMGCR myopathy, who has a relapsing and refractory disease course despite intense immunosuppressive therapies, and analyze the previously published cases.
Why is it important?
Anti-HMGCR myopathy should be kept in mind in patients with juvenile idiopathic inflammatory myopathies, especially in the presence of proximal muscle weakness prominent in the lower extremities, markedly elevated serum CK levels, muscle biopsy demonstrating necrotizing features, negative myositis specific antibody profile, muscle MRI signatures, and refractory disease course. Although suggestive, these findings do not always correlate with clinical relapses. On the other hand, the spectrum is expanded with patients presenting with a muscular dystrophy phenotype. Anti-HMGCR myopathy is an uncommon cause of myopathy in children but has treatment. Therefore, it is very important to consider testing for anti-HMGCR autoantibodies in children presenting with subacute, new-onset proximal muscle weakness and/or in the case of a genetically not confirmed myopathy or muscular dystrophy. The outcome is affected by the duration between the disease onset and the initiation of treatment. Thus, early diagnosis and treatment are highly valuable in this disease. However, although spontaneous remission is reported in rare pediatric cases, anti-HMGCR myopathy is not benign and can be relapsing and refractory. There is a need for prospective studies on the long-term efficacy of the currently available drugs, new therapeutic approaches and when to stop escalating immunosuppressive treatments.