denervation

Denervation is loss of nerve supply to a muscle, organ, or region, resulting in diminished function of motor, sensory, or autonomic pathways. It can result from damage to a peripheral nerve, a nerve root, or loss of motor neurons in the spinal cord or brain, interrupting neural input to the target tissue. Distal to a lesion, axons degenerate (Wallerian degeneration), and denervation of autonomic fibers can alter vascular or glandular control.

Causes include traumatic nerve injury (laceration or crush), surgical transection, severe compression, or chronic neuropathies in diabetes or inflammatory disorders. Denervation can affect peripheral nerves, nerve roots, or motor neurons in the spinal cord, leading to loss of input to target tissues.

Pathophysiology involves Wallerian degeneration of the distal axon and degeneration of motor endplates. Proximal nerve stumps can sprout regenerating axons that may reinnervate if distance and environment permit; prolonged denervation reduces reinnervation potential and leads to muscle fiber loss and remodeling.

Clinically, denervated muscles show weakness and rapid atrophy; reflexes are reduced; fasciculations may occur. EMG reveals fibrillation potentials and positive sharp waves in denervated muscle; nerve conduction may be reduced or absent across the lesion. Imaging helps identify structural causes.

Management focuses on treating the underlying cause and restoring nerve input when possible with surgical repair, nerve grafts, or nerve transfers; rehabilitation and electrical stimulation can help. Prognosis depends on cause and distance; regeneration occurs at roughly 1–3 mm per day and decreases with time.