(See also Overview of Peripheral Nervous System Disorders Overview of Peripheral Nervous System Disorders The peripheral nervous system refers to parts of the nervous system outside the brain and spinal cord. It includes the cranial nerves and spinal nerves from their origin to their end. The anterior... read more .)
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.
Symptoms and Signs of HNPP
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 Peroneal nerve palsy Single mononeuropathies are characterized by sensory disturbances and weakness in the distribution of the affected peripheral nerve. Diagnosis is clinical but may require confirmation with electrodiagnostic... read more 
with footdrop, ulnar nerve palsy Ulnar nerve palsy Single mononeuropathies are characterized by sensory disturbances and weakness in the distribution of the affected peripheral nerve. Diagnosis is clinical but may require confirmation with electrodiagnostic... read more , and carpal tunnel syndrome Carpal tunnel syndrome Single mononeuropathies are characterized by sensory disturbances and weakness in the distribution of the affected peripheral nerve. Diagnosis is clinical but may require confirmation with electrodiagnostic... read more 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.
Diagnosis of HNPP
Electrodiagnostic testing
Genetic testing
Hereditary motor neuropathy with liability to pressure palsies should be suspected in patients with any of the following:
Recurrent compression mononeuropathies
Multiple mononeuropathy of unknown origin
Symptoms suggesting recurrent demyelinating polyneuropathy (eg, chronic inflammatory demyelinating polyneuropathy [CIDP])
A family history of carpal tunnel syndrome
Electrodiagnostic testing and genetic testing aid in diagnosis; rarely, biopsy is required.
Treatment of HNPP
Supportive care
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.
Key Points
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 recurrent demyelinating 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.
