A Case of Filamin C Proximal Myopathy

Joy Chan MD, Perry Shieh MD, PhD
1. University of California, Los Angeles, 2. University of California, Los Angeles

Background: Filamin C (FLNC) myopathies present with a diverse range of phenotypes with the proximal form presenting with proximal weakness and pathology consistent with myofibrillar myopathy. Filamin C myopathy should be considered in patients presenting with proximal weakness and history of autosomal dominant inheritance. Respiratory and cardiac involvement is common.

Objectives: We describe a patient who presented with slowly progressive proximal weakness and family history of similar symptoms found to have an autosomal dominant mutation in filamin C and emphasize diagnosis and management of this disease.

Approach: A 48-year-old woman presented with 1 year of progressive proximal weakness in her arms and legs with extensive family history notable for similar symptoms in her father, paternal uncle, and paternal grandmother. Exam showed MRC grade 4/5 strength in bilateral deltoids and iliopsoas.

Results: CK was 532. Outside EMG/NCS showed myopathic changes. Muscle biopsy showed chronic active myopathy with histology consistent with myofibrillar myopathy. Genetic testing revealed a heterozygous nonsense mutation p.W2710X in the filamin C gene. Management is supportive with cardiac monitoring, pulmonary function tests, and sleep study with CO2 monitoring to assess for respiratory involvement.

Conclusions: FLNC myofibrillar myopathy is an autosomal dominant disorder that presents in adulthood with slowly progressive proximal weakness that progresses to involve respiratory muscles. About 1/3 of these patients will have cardiac involvement. These patients should be assessed for cardiac and respiratory involvement over the course of their disease.