Polymyositis with Mitochondrial Pathology (PM-Mito)

Clinical features:

(1) adult onset

(2) symmetrical proximal muscle weakness

(3) slow progression

(4) variable (often poor) response to corticosteroid therapy

Muscle biopsy shows

(1) endomysial lymphocytic inflammation and myopathic change.

(2) increased numbers of cytochrome c oxidase (COX)-deficient fibers for age

(3) positive aggregates of LC3 and alphaB-crystallin

(4) little evidence of TDP-43 positive aggregates

There are large scale deletions in mitochondrial DNA.