Case

A 59-year-old man developed progressive swelling, stiffness and pain in the right anterior leg, 3 years after a right L4–L5 discectomy that had fully resolved his radicular symptoms. An anterior tibial fasciotomy, for presumed compartment syndrome, failed to lessen his symptoms. On examination, there was marked hypertrophy of the right anterior tibial musculature resulting in a 3 cm difference in leg circumference (figure 1). This limited his range of ankle joint movement, but there was no weakness. His serum creatine kinase was elevated (400 IU/L, normal <70), MR scan of the lower legs showed markedly enlarged right tibialis anterior muscle and biopsy of this muscle showed fibre splitting, fibre hypertrophy and central nuclei (figure 2). With no fibre-type grouping, the biopsy could not confirm reinnervation. His first electromyography (EMG) appointment was 3 years after the onset of the swelling, which had continued to worsen. Continuous complex repetitive discharges were recorded from all sites in the resting right tibialis anterior that were studied by concentric needle EMG (figure 3). The discharges occurred spontaneously and were also enhanced by needle movement. Jitter between individual action potentials within the complex repetitive discharges complexes, measured using single fibre EMG, was often very low (figure …