Hereditary Motor Neuropathy With Liability to Pressure Palsies (HNPP)
(See also Overview of Peripheral Nervous System Disorders.)
In HNPP, peripheral nerves lose their myelin sheath and do not conduct nerve impulses normally. Inheritance is usually autosomal dominant. In 80%, the cause is loss of one copy of peripheral myelin protein-22 gene (PMP22), located on the short arm of chromosome 17. Two copies of the gene are needed for normal function.
Incidence of HNPP is estimated to be 2 to 5/100,000.
Usually, symptoms of hereditary motor neuropathy with liability to pressure palsies start during adolescence or young adulthood, but they may start at any age.
Peroneal nerve palsy with footdrop, ulnar nerve palsy, and carpal tunnel syndrome commonly develop. The pressure palsies can be mild or severe and last from minutes to months. Numbness and weakness occur in affected areas.
After an episode, about half of affected people completely recover, and symptoms are mild in most of the rest.
Hereditary motor neuropathy with liability to pressure palsies should be suspected in patients with any of the following:
Electrodiagnostic testing and genetic testing aid in diagnosis; rarely, biopsy is required.
Treatment of hereditary motor neuropathy with liability to pressure palsies involves avoiding or modifying activities that cause symptoms. Wrist splints and elbow pads can reduce pressure, prevent reinjury, and allow the nerve to repair the myelin over time.
Surgery is rarely indicated.
Hereditary motor neuropathy with liability to pressure palsies (HNPP) is a rare, usually autosomal-dominant disorder.
Consider HNPP if patients have unexplained peripheral mononeuropathies (eg, peroneal or ulnar nerve palsy, carpal tunnel syndrome) or symptoms consistent with chronic inflammatory polyneuropathy.
Diagnose using electrodiagnostic testing and genetic testing.
Advise patients to avoid or modify activities that cause symptoms, and recommend wrist splints and/or elbow pads as needed.