Distal Myopathy in Multi-minicore Disease

A 52-year-old man noted distal dominant slowly progressive muscle weakness at age 36 years. On muscle CT, the red muscles of the soleus, anterior tibial and paraspinal muscles, where type 1 fiber is known to predominate, were almost totally replaced by fat tissue while quadriceps femoris, gastrocnemius and upper extremity muscles were relatively spared. Quadriceps muscle biopsy revealed multi-minicores in addition to occasional larger cores, in about 70% of the type 1 fibers. A novel heterozygous nucleotide change c.5869T > A (p.S1957T) was identified in RYR1. Although pathogenicity was not confirmed, this nucleotide change was absent in 100 control DNA. We did not find a mutation in either multi-minicore disease-associated gene, SEPN1, or major distal myopathy-related genes, including GNE, ZASP, MYOT, exons 32-36 of MYH7, and the last exon of TTN. This is probably a unique form of distal myopathy characterized by the presence of multi-minicores with preferential involvement of type 1 fibers.