Bilateral Ulnar Neuropathy Secondary to Chronic Pentazocine Injections: A Rare Neurological Sequela of Substance Abuse.

Ulnar neuropathy (UN) is the second most common entrapment neuropathy, typically resulting from trauma, fractures, compression, dislocations, repetitive elbow movements, or congenital malformations secondary to previous injuries. However, it may also arise as a complication of substance abuse. We report the case of a 45-year-old male with bilateral ulnar neuropathy secondary to 22 years of intravenous pentazocine (Sosegon) abuse, highlighting repeated local tissue injury and fibrosis as potential pathogenic factors. The patient presented with progressive swelling, numbness, and pain in both upper extremities, along with a bilateral flexion contracture of the left fourth and fifth digits. Nerve conduction studies (NCS) revealed severe left ulnar neuropathy at the elbow distal to the branch of the flexor carpi ulnaris, and moderate-to-severe right ulnar neuropathy at the elbow proximal to the same branch. Needle electromyography (EMG) demonstrated significant denervation in muscles innervated by the ulnar nerve. After preoperative evaluation, the patient underwent successful ulnar nerve transposition followed by physiotherapy, resulting in symptomatic improvement at six-month follow-up. This case highlights chronic pentazocine abuse as a rare but significant cause of bilateral ulnar neuropathy, likely due to repeated local trauma and fibrosis. Early recognition and a multidisciplinary management strategy involving neurosurgery, addiction medicine, and physiotherapy to address both the neurological sequelae and the underlying substance abuse are essential to optimizing long-term functional and clinical outcomes.