A 47-year-old white male with a background history of chronic left sciatic pain developed a lump on the left thigh. Muscle MRI showed changes consistent with myotome L5 hypertrophy, while a lumbosacral MRI showed a disc protrusion at L4-L5. Continuous complex repetitive discharges became evident through needle electromyogram with a muscle biopsy showing chronic denervation changes. Botulinum toxin (BT) administered for a year produced a signifcant electrophysiological improvement. This is a rare case of BT responsive L5 radicular denervation hypertrophy involving the muscle tensor fascia lata.