Magnetic resonance spectroscopy and histological study of tubular aggregates in a familial myopathy.

31-P MR spectroscopy has been used to investigate metabolic events surrounding muscular contraction in a patient with an unusual myopathy characterized by clinical signs of muscle stiffness and swelling after prolonged exercise. Histological assays demonstrated a predominance of type II fibers with tubular aggregates. These structures had low calcium content although calcium-ATPase protein was present. Metabolic measurements were normal at rest except for the presence of a marked signal in the phosphodiester region which could reflect membrane abnormalities. Exercise-induced PCr consumption was in the normal range but the extent of the related intracellular acidosis was abnormally large. Kinetics of PCr and PCr/Pi ratio post-exercise recovery were delayed, but were likely to reflect the effect of the very low end-of-exercise pH rather than an aerobic deficiency. Finally, proton efflux from muscle to bloodstream, measured during the initial recovery period, was delayed, indicating altered mechanisms of proton handling. The most prominent metabolic abnormality recorded is the large glycogenolysis-induced pH decrease which might be linked to either abnormal activation of glycogenolysis and/or impaired proton and lactate handling within the muscle. The association between tubular aggregates and hyperacidosis is of interest but the exact causal relationship remains to be elucidated.