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Hereditary Motor Neuropathy With Liability to Pressure Palsies (HNPP)

(Tomaculous Neuropathy)

By Michael Rubin, MDCM

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Patient Education

In hereditary motor neuropathy with liability to pressure palsies (HNPP), nerves become increasingly sensitive to pressure and stretch.

In HNPP, 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

Usually, symptoms 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.


  • Electrodiagnostic testing

  • Genetic testing

HNPP should be suspected in patients with any of the following:

  • Recurrent compression mononeuropathies

  • Multiple mononeuropathy of unknown origin

  • Symptoms suggesting recurrent demyelinating polyneuropathy

  • A family history of carpal tunnel syndrome

Electrodiagnostic testing and genetic testing aid in diagnosis; rarely, biopsy is required.


  • 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.

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