Hereditary neuropathy with liability to pressure palsies

Alternate names

HNPP; Polyneuropathy, familial recurrent; Tomaculous neuropathy

Definition

Hereditary neuropathy with liability to pressure palsies (HNPP) is a disorder that affects peripheral nerves, causing the nerves to be highly sensitive to pressure.

Cause

• Hereditary neuropathy with liability to pressure palsies is caused by mutations in the PMP22 gene.
• The condition results when one gene is either missing or altered.
• While not completely understood, it is believed that mutations in the PMP22 gene affect myelin, the protective substance that covers nerve cells.
• As a result of these mutations, some of the protective myelin which covers the nerves becomes unstable, leading to the increased sensitivity to pressure on the nerves.

Inheritance

Autosomal dominant pattern, a 50/50 chance.

• Hereditary neuropathy with liability to pressure palsies (HNPP) is inherited in an autosomal dominant manner. This means that having a deletion or change (mutation) in only one copy of the responsible gene in each cell is enough to cause features of the disorder. There is nothing that either parent can do, before or during a pregnancy, to cause a child to have HNPP.
• In some cases, a person with HNPP inherits the deletion or mutation from a parent with HNPP. In other cases, HNPP occurs for the first time in a person with no family history of the disorder. When a person with HNPP has children, each child has a 50% (1 in 2) chance to have HNPP.

Onset

Symptoms usually begin during adolescence or early adulthood but may develop anytime from childhood to late adulthood. Symptoms vary in severity.

Signs and symptoms

• The most common problem sites involve nerves in the wrists, elbows, and knees; however, the fingers, shoulders, hands, feet, and scalp can also be affected. Symptoms associated with HNPP occur in episodes, due to pressure on any single peripheral nerve.
• Symptoms may include numbness, tingling, and/or loss of muscle function (palsy), pain in the limbs (especially the hands), carpal tunnel syndrome (impairing the ability to use the fingers, hands, and wrists), and foot drop (making it hard or impossible to walk, climb stairs, or drive).
• Some people experience fatigue, generalized weakness, muscle cramps, pain in the muscles or bones, or lower back pain.
• An episode of symptoms associated with HNPP can last from several minutes to days or even months.
• Most people completely recover after an episode, but repeated episodes can cause permanent muscle weakness or loss of sensation.

Clinical presentation

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

80%-99% of people have these symptoms

• Decreased motor nerve conduction velocity

30%-79% of people have these symptoms

• Paresthesia(Pins and needles feeling)
• Scoliosis

5%-29% of people have these symptoms

• Cranial nerve paralysis
• Hyporeflexia(Decreased reflex response)
• Pes cavus(High-arched foot)
• Respiratory insufficiency(Respiratory impairment)
• Vocal cord paralysis(Inability to move vocal cords)

Diagnosis

The hereditary neuropathies can be diagnosed by blood tests for genetic testing, nerve conduction studies, and nerve biopsies.

Treatment

• There is no specific treatment for hereditary neuropathy with liability to pressure palsies (HNPP).
• Management is based on each person's symptoms and severity.
• Some people use braces, such as a wrist splint, or ankle-foot orthosis (for foot drop).
• Protective pads worn at the elbows or knees may prevent pressure and trauma to local nerves.
• In general, people with HNPP should try to avoid positions and activities that cause pressure on the nerves, such as prolonged sitting (particularly with the legs crossed), leaning on the elbows, occupations requiring repetitive movements of the wrist, and tying shoes too tightly.
• For mild pain, over-the-counter pain medicines may be used.
• For more severe pain, prescription drugs used for peripheral neuropathy may be used.

NIH genetic and rare disease info

• NIH info on Hereditary neuropathy with liability to pressure palsies

Hereditary neuropathy with liability to pressure palsies is a rare disease.

Hereditary neuropathy with liability to pressure palsies Resources
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