CT-negative, MRI GRE-positive primary motor cortex contusion causing isolated foot drop

BACKGROUND Isolated acute foot drop due to traumatic brain injury is exceedingly rare and is often misdiagnosed during initial evaluation. Here, we present the case of a patient who presented with left foot drop after falling off a bicycle. CASE DESCRIPTION The patient is a 55-year-old male who was mountain biking when he fell, hit his head, and lost consciousness. Neurologic examination of the left leg revealed foot drop, no sensory deficits, and 3+ reflexes at the knee and ankle with clonus. Electroencephalography, computed tomography (CT) of the head, magnetic resonance imaging (MRI) of the lumbar spine, and CT of the lower extremities were all negative. Only MRI of the brain with a gradient echo sequence revealed microhemorrhages focused around the right precentral gyrus. The patient underwent physical therapy, and by 3 months had regained full strength in his left leg. CONCLUSION Central causes of foot drop are exceptionally rare, however, they should be considered in all cases of post-traumatic dorsiflexion paresis. The key to the accurate diagnosis is a high index of suspicion as well as thorough and careful physical examination including reflex and sensory testing. Selective imaging modalities such as MRI or CT can then be used to verify the diagnosis.