Tubular aggregates in autoimmune Lambert-Eaton myasthenic syndrome

Abstract

Tubular aggregates are accumulations of densely packed tubules in muscle fibers, occurring in distinct hereditary and acquired disorders. We present a patient with tubular aggregates and autoimmune Lambert-Eaton myasthenic syndrome. Initially, he showed mild proximal weakness, borderline decrement on 3 Hz stimulation, and slightly elevated creatine kinase. Muscle biopsy revealed tubular aggregates in type II fibers. Due to a good response to pyridostigmine, a limb-girdle myasthenia with tubular aggregates was suspected, but genetic analyses of GFPT1, DPGAT1, and ALG2 were normal. Two years later, the patient presented with progressive weakness and autonomic dysfunction. 17% decrement on 3 Hz stimulation and 100% increment after brief exercise were revealed. Autoantibodies to voltage-gated calcium-channels confirmed the diagnosis of Lambert-Eaton myasthenic syndrome. Steroids, azathioprine, and 3,4-diaminopyridine significantly improved symptoms. No tumor was found during follow-up. This is the first report about tubular aggregates associated with an acquired myasthenic syndrome. Our findings are important because of the therapeutic implications.

Keywords: Acquired; Lambert–Eaton myasthenic syndrome; Muscle biopsy; Tubular aggregates.