Causes of unilateral foot drop and steppage gait include peroneal nerve palsy and L5 radiculopathy. Causes of bilateral foot drop and steppage gait include ALS, CMT disease and other severe peripheral neuropathies, and certain forms of muscular dystrophy. This patient had severe CMT disease with marked atrophy below the knee and 0/5 strength in the foot dorsiflexors bilaterally. There is also marked atrophy of the hand muscles.
Sensory ataxia may also cause a steppage gait because the patient lifts the feet up high and then slaps or stamps them down smartly to improve proprioceptive feedback. The gait of sensory ataxia may also cause a double tap but in that case the heel strikes first and smartly as the patient stamps the foot to the ground to improve proprioceptive feedback. The sound of the two varieties of double tap is quite different. A pronounced steppage gait due to foot drops is much more common than a steppage gait from sensory ataxia. In severe polyneuropathies, the steppage gait may have components of both sensory ataxia and foot drop.
Campbell WW. Clinical signs in neurology : a compendium. Philadelphia: Wolters Kluwer Health, 2016.
Campbell WW. DeJong's the neurologic examination, 7th ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2013.
Maranhao-Filho P, Maron RM, de Rosso AL. Teaching Video NeuroImage: Waddling-steppage gait secondary to spinal arachnoid cyst: an exceptional surgical outcome. Neurology 2008;70:e85.