Prognosis in AZT myopathy.

The myopathy caused by zidovudine (AZT) appears to be common but is incompletely characterized, particularly regarding prognosis. Twenty patients with HIV infection developed a necrotizing myopathy while taking AZT for 9 to 30 months. Ten presented with myalgia and 17 with proximal muscle weakness. Serum CK was elevated in all (two to 11 times normal), and EMG suggested active myopathy in all but two. There were scattered granular degenerating fibers, with scant or no inflammation, in a pattern consistent with a toxic myopathy in all 18 patients biopsied. Three patients with an HIV-related inflammatory myopathy were distinguished by histologic differences. After stopping AZT (n = 15), myalgia promptly resolved (10 of 10). Strength improved more slowly with 12 of 15 regaining normal or nearly normal strength, but three have persistent weakness. CK returned to normal in 12 of 15, and follow-up EMG (n = 11) documented reduced fibrillation density in all 11 patients. These findings underscore the need for early diagnosis of this reversible myopathy.