Dominantly inherited myopathy with novel tubular aggregates containing 1-21 tubulofilamentous structures

Tubular aggregates (TAs) in skeletal muscle fibers have been observed as a nonspecific finding in a number of different conditions such as periodic paralysis, myotonic disorders, hyperaldosteronism, chronic use of drugs, and alcoholism. However, TAs were also found more specifically in well-defined muscle disorders, e.g., exercise-induced cramps, myasthenic syndromes, and even in dominantly or recessively inherited familial myopathies. We report on a presumably dominantly inherited familial myopathy with late onset characterized morphologically by the presence of three types of TAs in type II muscle fibers identified in three affected members of one family (a 86-year-old man and his two sons). The first, novel type was characterized by tubules, 30-200 nm in thickness which included 1-21 tubulofilamentous structures 14-18 nm in diameter. The second type of TAs corresponded to previously well-described tubules and were derived from terminal cisternae, which were rather irregularly arranged or widened, and filled with material of medium electron density. The third type of TAs were occasional, hexagonally arranged TAs of the usual type [type Ib and Ic]. Rare annulate lamellae were also seen. Our findings support the evidence of tubular aggregates as the major finding in certain dominantly inherited myopathies. Tubules of the first type, to the best of our knowledge, have not been recorded in any other myopathy. It is therefore suggested that these tubules characterize a novel type of a benign, slowly progressive myopathy with late onset, muscle pain, cramps, and stiffness.