Pathogenic variants in the skeletal muscle α-actin 1 gene (ACTA1) cause a spectrum of myopathies with clinical and myopathological diversity. Clinical presentations occur from the prenatal period to adulthood, commonly with proximal-predominant weakness and rarely preferential distal weakness. Myopathological findings are wide-ranging, with nemaline rods being most frequent. Associated cardiomyopathy is rare and conduction defects are not reported. We describe a family with congenital myopathy with prominent finger flexor weakness and cardiomyopathy with cardiac conduction defects. The proband, a 48-year-old Caucasian male, his 73-year-old mother, 41-year-old sister, and 19-year-old nephew presented with prominent finger flexor weakness on a background of neonatal hypotonia and delayed motor milestones. All had progressive cardiomyopathy with systolic dysfunction and/or left ventricular dilation. The proband and sister had intraventricular conduction delay and left anterior fascicular block, respectively. The mother had atrial fibrillation. Muscle biopsy in the proband and sister demonstrated congenital fiber-type disproportion and rare nemaline rods in the proband. A novel dominant variant in ACTA1 (c.81C>A, p.Asp27Glu) segregated within the family. This family expands the genotypic and phenotypic spectrum of ACTA1-related myopathy, highlighting preferential finger flexor involvement with cardiomyopathy and conduction disease. We emphasize early and ongoing cardiac surveillance in ACTA1-related myopathy.

Muscle 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.

The patient was an 81-year-old woman. At age 73, she developed difficulties in climbing stairs and swallowing, and became unable to open bottles at age 74. She had been walking with a cane since age 76. Accidental chest X-ray findings showed bilateral hilar lymphadenopathy at age 78. Angiotensin converting enzyme (ACE) was elevated. Lymphocyte proliferation was prominent in bronchoalveolar lavage fluid. Sarcoidosis was suspected, but she was followed without treatment due to lack of respiratory symptoms. She became unable to walk without assistance at age 80 and visited our hospital with a complaint of gait disturbance at age 81. Moderate diffuse muscle atrophy in extremities was evident. Muscle weakness of finger flexion and knee extension were remarkable. The muscle involvement pattern was similar to sporadic inclusion body myositis (sIBM). However, radiographically, rectus femoris and semitendinosus muscles are selectively preserved. This radiogaphic finding was consistent with chronic sarcoid myopathy (CSM). We reached a final diagnosis of CSM based on the presence of granulomas in the muscle biopsy specimen, BHL in fluorodeoxyglucose positron-emission tomography, the previous finding of elevated ACE, and bronchoscopy results. In conclusion, CSM is a treatable disease and should thus be differentiated from sIBM. This should not be done solely based on clinical findings, but instead, muscle biopsy should be performed. Moreover, muscle selectivity may be useful in distinguishing between CSM and sIBM.

Actinopathy is a group of clinically and pathologically heterogeneous myopathies due to mutations in the skeletal muscle sarcomeric α-actin 1-encoding gene (ACTA1). Disease-onset spans from prenatal life to adulthood and weakness can preferentially affect proximal or distal muscles. Myopathological findings include a spectrum of structural abnormalities with nemaline rods being the most common. We report a daughter and father with prominent finger flexors and/or quadriceps involvement. Muscle biopsies revealed rimmed vacuoles in both patients, associated with type 1 fiber atrophy in the daughter, and nemaline rods in the father. Next generation sequencing identified a novel dominant ACTA1 variant, c.149G>A (p.Gly50Asp) in both individuals and no abnormal variants in vacuolar myopathy-associated genes. Our findings expand the clinico-pathological spectrum of actinopathy.

BACKGROUND: The aim of this study was to characterize a unique distribution of muscle involvement in sporadic Becker muscle dystrophy (BMD).
METHODS: Retrospective chart review, clinical examination, electrophysiological studies, cardiac testing, and genetic testing were performed in 5 patients.
RESULTS: Predominant weakness and atrophy of biceps brachii, hip adduction, and quadriceps muscles was noted along with calf and extensor forearm hypertrophy. Finger flexor muscles were severely weak in 3 of 5 patients, a feature that could lead to a misdiagnosis of inclusion body myositis. Creatinine kinase was only mildly elevated in most patients. Electromyography was abnormal in all patients. Muscle biopsy in 1 patient demonstrated normal immunostaining for dystrophin.
CONCLUSIONS: We found a unique and uniform distribution of muscle involvement in 5 sporadic cases of BMD. Recognizing these features is important for differentiating it from other myopathies that may have similar features and avoids unnecessary invasive procedures such as muscle biopsy.