Muscle protein synthesis in steroid-induced proximal myopathy: a case report.

A 51-year-old man with proven adenosquamous carcinoma of the lung presented with clinically acute steroid myopathy. Postabsorptive whole body leucine kinetics and fractional mixed muscle protein synthesis rate (MPSR) were determined by a steady-state approach during continuous L-(1-13C) leucine infusion. Plasma 13C alpha-ketoisocaproic acid enrichment was taken to represent labeling of the precursor pool. Postabsorptive whole body leucine flux and protein synthesis were less than the 1 in 500 confidence intervals of control values. Fractional MPSR was significantly reduced (P less than 0.01). Simultaneous calculation of MPSR from two adjacent sites was in excellent agreement (0.0372 and 0.0395% h-1). This is the first report that steroid myopathy is associated with reduced whole body protein synthesis and fractional MPSR in man.