Hereditary Pressure Neuropathy (HNPP)

Characteristics

Hereditary pressure neuropathy (HNPP) is characterized by an increased vulnerability of nerves to pressure. This condition can cause sudden, painless paralysis or a “tingling” sensation in the limbs. Symptoms can vary widely, even within the same family, and in some individuals, they may be so mild that the condition goes unnoticed.

Prevalence and Disease Course

In the Netherlands, HNPP is estimated to affect approximately 1,000 people. Symptoms typically appear between the ages of 20 and 40, although they can occasionally manifest in childhood.

Key symptoms include transient, painless muscle paralysis and a “numb” sensation in the skin of the arms and legs, often triggered by pressure on superficial nerves. Common triggers include squatting, sitting cross-legged, kneeling, or leaning on the elbows. Medical procedures involving pressure, such as those requiring anesthesia, casts, or knee bandages, can also cause nerve impairment.

In most cases, the paralysis resolves within hours, days, or weeks. However, frequent episodes can lead to permanent nerve damage, resulting in symptoms similar to those seen in Charcot-Marie-Tooth disease (CMT/HMSN) Types 1 and 2, such as high arches, muscle weakness in the feet and lower legs, and visibly thinner calves.

Cause

The heightened sensitivity of nerves to pressure in HNPP is due to a defect in the myelin sheath, the insulating layer surrounding peripheral nerve fibers. In HNPP, the myelin sheath is abnormally structured and thickened in certain areas, causing delayed signal transmission between the spinal cord and muscles or between the skin and joints and the spinal cord.

The condition is caused by the absence of a DNA fragment on chromosome 17. This genetic defect is inherited in an autosomal dominant manner, meaning each child of an affected parent has a 50% chance of inheriting the condition.

Treatment

HNPP cannot be cured, but symptoms can be managed or prevented. Individuals with the condition are advised to avoid postures and activities that place excessive pressure on nerves.

For those with chronic nerve damage, assistive devices or home adaptations may be necessary. A rehabilitation physician and occupational therapist can provide tailored advice to support daily functioning and improve quality of life.