A Case of Intermittent Exercise-Induced Foot Drop in a Recreational Runner.

Foot drop is a reduction in ankle dorsiflexion during the swing phase of gait. We report a case of a 51-year-old recreational runner and cyclist who presented with intermittent left foot drop initially triggered by running distances in excess of 10 km. The patient was investigated with magnetic resonance imaging (MRI) of the spine and leg, nerve conduction studies, electromyography, and compartment pressure testing, which were all normal. Surgical release of fascia, which was restricting the common peroneal (fibular) nerve, failed to resolve her symptoms. Subsequent brain MRI revealed demyelination. This case describes the unusual case of a recreational runner presenting with exercise-induced foot drop secondary to multiple sclerosis (MS). Motor fatigability is a common feature of MS, and this case highlights the need to remain cognizant of central and peripheral causes of exertional lower limb pathology, particularly in the absence of pain.