Some cases of foot drop are temporary and others are permanent. Causes of foot drop are numerous, but the most common cause is an injury to the peroneal nerve at the top of the calf behind the knee. Other causes of foot drop include multiple sclerosis, Parkinson’s disease, amyotrophic lateral sclerosis (ALS) Lou Gehrig’s disease, and muscular dystrophy. Additional causes include stroke, drug toxicity, diabetes, low back pain, and cauda equine, a compression of the lower bundle of nerves in the spinal cord.