Nicolau, Stefan

AbstractMuscle disorders are characterized by differential involvement of various muscle groups. Among these, weakness predominantly affecting finger flexors is an uncommon pattern, most frequently found in sporadic inclusion‐body myositis. This finding is particularly significant when the full range of histopathological findings of inclusion‐body myositis is not found on muscle biopsy. Prominent finger flexor weakness, however, is also observed in other myopathies. It occurs commonly in myotonic dystrophy types 1 and 2. In addition, individual reports and small case series have documented finger flexor weakness in sarcoid and amyloid myopathy, and in inherited myopathies caused by ACTA1, CRYAB, DMD, DYSF, FLNC, GAA, GNE, HNRNPDL, LAMA2, MYH7, and VCP mutations. Therefore, the finding of finger flexor weakness requires consideration of clinical, myopathological, genetic, electrodiagnostic, and sometimes muscle imaging findings to establish a diagnosis.

AbstractMutations in glycogenin‐1 (GYG1) cause an adult‐onset polyglucosan body myopathy. We report here a patient presenting with late‐onset distal myopathy. We wish to highlight this rare clinical phenotype of GYG1‐related myopathy and the histological clues leading to its diagnosis.

See article on pages 739–744 in this issue.

AbstractAlthough myopathies and neuromuscular junction disorders are typically distinct, their coexistence has been reported in several inherited and acquired conditions. Affected individuals have variable clinical phenotypes but typically display both a decrement on repetitive nerve stimulation and myopathic findings on muscle biopsy. Inherited causes include myopathies related to mutations in BIN1, DES, DNM2, GMPPB, MTM1, or PLEC and congenital myasthenic syndromes due to mutations in ALG2, ALG14, COL13A1, DOK7, DPAGT1, or GFPT1. Additionally, a decrement due to muscle fiber inexcitability is observed in certain myotonic disorders. The identification of a defect of neuromuscular transmission in an inherited myopathy may assist in establishing a molecular diagnosis and in selecting patients who would benefit from pharmacological correction of this defect. Acquired cases meanwhile stem from the co‐occurrence of myasthenia gravis or Lambert‐Eaton myasthenic syndrome with an immune‐mediated myopathy, which may be due to paraneoplastic disorders or exposure to immune checkpoint inhibitors.