In hereditary motor neuropathy with liability to pressure palsies (HNPP), nerves become increasingly sensitive to pressure and stretch.
In HNPP, peripheral nerves develop structural and functional abnormalities of the myelin sheath resulting in abnormal nerve conduction. Inheritance is usually autosomal dominant. In most patients, the cause is loss of 1 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.
HNPP is rare.
Symptoms and Signs of HNPP
Symptoms of HNPP usually start during adolescence or young adulthood, but they may start at any age.
HNPP commonly affects nerves that are superficial and pass near bony prominences, which are areas where the nerves are vulnerable to external compression. Peroneal nerve palsy with footdrop, ulnar nerve palsy, and carpal tunnel syndrome develop after some period of nerve compression. 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 patients completely recover, and symptoms are mild in most of the rest.
Diagnosis of HNPP
Electrodiagnostic testing
Genetic testing
HNPP should be suspected in symptomatic 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 HNPP 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.
