Hereditary Neuropathy With Liability to Pressure Palsies (HNPP)
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.
(See also Overview of the Peripheral Nervous System.)
Usually, this neuropathy starts during adolescence or young adulthood, but it may start at any age. It affects both sexes equally.
Hereditary neuropathy with liability to pressure palsies is usually inherited as an autosomal (not sex-linked) dominant trait. That is, only one gene from one parent is required for the disease to develop.
In this neuropathy, nerves lose their myelin sheath (called demyelination) and do not send nerve impulses normally. (The myelin sheath functions much like insulation around electrical wires, enabling nerve impulses to travel quickly.)
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 may be 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.
Doctors may have difficulty diagnosing hereditary neuropathy with liability to pressure palsies because the symptoms come and go. Electromyography and genetic testing help establish the diagnosis.
Rarely, biopsy of a nerve is required.