Hereditary neuropathy with liability to pressure palsy

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Hereditary Neuropathy with Liability to Pressure Palsy (HNPP) is a peripheral neuropathy (disorder of the nerves).

Nerve with myelin sheath

General description

HNPP is a nerve disorder that affects the peripheral nerves. The main effect of HNPP are pressure palsies. Pressure on the nerves can cause tingling sensations, numbness, pain, weakness, muscle atrophy, and even paralyzation of affected area.

In normal individuals these symptoms disappear quickly but in sufferers of HNPP even a short period of pressure can cause the symptoms to occur. These usually subside over an extended period of time. Palsies can last from minutes, day to weeks or even months or years. However repeated incidents can cause permanent muscle weakness.

HNPP evolves slowly with symptoms surfacing between usually in the late teens to early twenties (range 8 to 64 years).[1]

The symptoms vary from person to person. Some report minor problems, whilst others experience severe discomfort and disability. In many cases the symptoms are mild enough to go unnoticed. The time period between episodes is known to vary between individuals. HNPP has not been found to alter the lifespan, although in some cases a decline in quality of life is noticed.

Some sufferers (10-15%) report various pains growing in severity with progression of the disease.[2]

The nerves most commonly affected are the peroneal nerve at the fibular head (leg and feet), the ulnar nerve at the elbow (arm) and the median nerve at the wrist (palm, thumbs and fingers), but any peripheral nerve can be affected.

HNPP is part of the group of Hereditary Motor and Sensory Neuropathy (HMSN) and is linked to Charcot–Marie–Tooth disease (CMT).

Diagnosis

Measuring nerve conduction velocities may give an indication of the presence of the disease, but HNPP can only be diagnosed by a genetic blood test. For fingers, it is often confused with carpal tunnel syndrome.

Symptoms

  • Back Pain
  • Pain at the sites of entrapment
  • Leg/ankle foot swelling
  • Fatigue
  • Muscle cramps
  • Paresthesias (abnormal sensations)
  • Muscle weakness
  • Foot drop
  • Numbness in fingers
  • Numbness in toes causing loss of balance

Causes

HNPP is an autosomal dominant genetic disease. A mutation in one copy of the gene PMP-22 (Peripheral myelin protein 22, 17p11.2) that makes the peripheral myelin protein causes haploinsufficiency, where the activity of the normal gene is insufficient to compensate for the loss of function of the other gene. The lack of myelin causes the nerves to be poorly insulated and it is this that causes symptoms. On visualization the nerves have a sausage like appearance that blocks the nerve signals (hence the name 'tomaculous neuropathy' that is sometimes used for HNPP).

Both male and females are equally affected. A child has a 50% chance of inheriting the disease if one parent is a sufferer of the disease. It is estimated that it occurs in 2 to 5 in 100000 individuals.

File:Nervous system diagram-en.svg

Cure

Currently there are no effective treatments but it is a possible candidate for gene therapy. Currently simple adjustments to the individuals lifestyle are the best treatment in order to avoid excess pressure on the nerves. Avoiding repetitive injury of a nerve is important, as this makes the symptoms worse. To reduce foot and leg swelling, lying with feet raised above hip level is recommended. For fingers, splints keeping the wrist and pals aligned can be prescribed for night use. Avoiding sleeping in foetal position is useful for all symptoms.

Common problems

There are lots of common problems, mainly caused by focused pressure on the nerves :

  • Kneeling
  • Cutting with scissors
  • Holding plastic grocery bags (or carrying anything that gives high pressure on one point)
  • Sitting with legs crossed
  • Leaning on elbows, forearms or wrists
  • Sleeping in the 'wrong' positions
  • Sitting too long in the same position
  • Walking in high heels
  • Being in the front leaning rest

History

Inherited peripheral nerve disorders were first described by Charcot, Marie and Tooth (1886). De Jong (1947) first described HNPP in a Dutch family. Dyck and Lambert (1968) showed nerve conduction slowing in families using electrophysiological studies. Chance et al. (1993) detected the chromosome deletion in most of the patients with HNPP.

External links

References

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