ICD-11

Damage to a single nerve or nerve group of the lower limb (not including central nervous structures such as the brain, brainstem or spinal cord), resulting in a loss of movement, sensation and/or autonomic function.

Lower limb mononeuropathy refers to pathology affecting a single peripheral nerve of the lower limb. The peripheral nerve may be damaged anywhere along its course from the spinal nerve root, as part of the lumbar plexus, or along its terminal branches. Damage results in weakness, disturbance of sensation, and/or pain. Generally, the term mononeuropathy refers to nerve damage occurring distal to the lumbosacral plexus. The most common mononeuropathies of the lower extremity are common peroneal neuropathy, sciatica, femoral neuropathy, meralgia paresthetica, and tarsal tunnel syndrome. These are usually due to mechanical injury caused by compression or trauma. Diabetes mellitus, connective tissue disorders and infections such as leprosy are some of the diseases considered in the aetiology of mononeuropathy. Compression of the common peroneal nerve at the head of fibula leads to foot drop, numbness over the dorsum of the foot, and weakness of eversion of the foot with sparing of ankle reflex. The most common cause of sciatica is compression by lower lumbar intervertebral discs. In complete sciatic paralysis, the knee cannot be flexed and all the muscles below the knee are paralyzed; partial compressive lesions are more common and tend to involve peroneal-innervated muscles more than tibial-innervated ones, giving the impression of a peroneal neuropathy. Compression of the lateral cutaneous nerve of thigh below the inguinal ligament leads to meralgia paresthetica. There is numbness, mild sensitivity to touch, and reduced touch and pinprick sensation in the territory of nerve; there is no weakness of the quadriceps or diminution of the knee reflex. The posterior tibial nerve may be compressed in the tarsal tunnel (“tarsal tunnel syndrome”); there is tingling, pain, and burning over the sole of the foot, usually without any motor deficits.