Merck Manual

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Hereditary Neuropathy With Liability to Pressure Palsies (HNPP)

(Tomaculous Neuropathy)


Michael Rubin

, MDCM, New York Presbyterian Hospital-Cornell Medical Center

Reviewed/Revised Apr 2022 | Modified Sep 2022

Hereditary neuropathy with liability to pressure palsies is a hereditary disorder in which nerves become increasingly sensitive to pressure, injury, and use.

  • In this disorder, nerves are easily damaged by slight pressure or injury or by repetitive use.

  • Numbness, tingling, and weakness occur in the affected area.

  • Electromyography and genetic testing help establish the diagnosis.

  • People should avoid or modify activities that cause symptoms, and wrist splints and elbow pads may help by reducing pressure on the affected nerves.

Usually, this neuropathy starts during adolescence or young adulthood, but it may start at any age. It affects both sexes equally.

In this neuropathy, nerves lose their myelin sheath (called demyelination Overview of Demyelinating Disorders Most nerve fibers inside and outside the brain are wrapped with many layers of tissue composed of a fat (lipoprotein) called myelin. These layers form the myelin sheath. Much like the insulation... read more ) and do not send nerve impulses normally. (The myelin sheath functions somewhat like insulation around electrical wires, enabling nerve impulses to travel quickly.)

Symptoms of HNPP

Hereditary neuropathy with liability to pressure palsies commonly affect nerves that run close to the body’s surface near a bone. For example, the following nerves are often affected:

Numbness, abnormal sensations (such as tingling), or weakness occurs periodically in the affected area. For example, peroneal nerve palsy weakens the muscles that lift the foot. As a result, people cannot lift the front part of their foot (a condition called footdrop) and may drag the front part of the foot along the ground as they walk.

Symptoms vary from unnoticeable and mild to severe and incapacitating. Episodes may last several minutes to months. They may recur, sometimes involving different nerves.

After an episode, about half of affected people recover completely, and most of the rest have mild symptoms.

Diagnosis of HNPP

  • Electromyography and nerve conduction studies

  • Genetic testing

Doctors may have difficulty diagnosing hereditary neuropathy with liability to pressure palsies because the symptoms come and go. Electromyography, nerve conduction studies Electromyography Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Imaging tests commonly used to diagnose nervous system (neurologic) disorders... read more Electromyography , and genetic testing help establish the diagnosis.

Rarely, biopsy of a nerve is required to look for areas of swelling along the nerve that typically occur in hereditary neuropathy.

Treatment of HNPP

  • Avoidance of activities that cause symptoms

  • Wrist splints and elbow pads

Activities that cause symptoms should be avoided or modified.

Supports, such as wrist splints and elbow pads, can reduce pressure, prevent reinjury, and allow the nerve to repair itself over time.

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