Muscle biopsies of 50 patients with postviral CFIDS .
Mild to severe atrophy of type II fibres in 39 biopsies, with a mild to moderate excess of lipid.
35 of these showed branching and fusion of mitochondrial cristae.
Mitochondrial degeneration was obvious in 40 of the biopsies with swelling, vacuolation, myelin figures and secondary lysosomes.
Control biopsies: even mild changes were rarely detected.