Late-Onset Proximal Myotonic Myopathy (PROMM): A Rare Presentation in an Adult

Proximal myotonic myopathy (PROMM) is normally associated with bilateral proximal weakness of lower limbs, slight elevation of liver enzymes, and cataracts. Myotonic dystrophy and PROMM are both autosomal dominant disorders, but gene study is completely normal in the case of PROMM. The most important differential diagnosis of PROMM is myotonic dystrophy. In our case, we reported late-onset PROMM in a patient 42 years old whose symptoms started at the age of 33 years; genetic evaluation of both myotonic dystrophy type 1 and myotonic dystrophy type 2 came out to be normal; therefore, the diagnosis of exclusion PROMM was made, which is a rare entity.