Prurigo nodularis (PN) is a skin condition in which hard crusty lumps form on the skin that itches intensely. PN may itch constantly, mostly at night, or only when a light brush of clothing sets off a round of severe itch. For many, itching only ends when the PN is scratched to the point of bleeding or pain.
A PN sore is hard, and usually about a half inch across. The top is dry and rough and often scratched open. Old white scars are often found nearby from old sores. They tend to be in the areas most easily reached: arms, shoulders and legs. There may be just a few or dozens.
PN, however, is actually the end result of scratching. Scratching causes the skin nerves to thicken, and when stimulated, they send unusually strong itch signals. Scratching is like "exercise" for the nerves, the more it is done, the stronger they become. What starts the scratching going at first can be different from one sufferer to the next. Once PN set in full force the end is similar, and it may last years.
Factors triggering PN, and keeping it going include nervous and mental conditions, reduced function of the liver and kidneys, and skin diseases such as eczema, bullous pemphigoid and dermatitis herpetiformis. In many patients, the true cause is never found.
Treatment is difficult. Due to the intensity of the itch patients often go from doctor to doctor looking for relief. No one treatment is always effective and several treatments may need to be tried. Initial treatment is often potent prescription steroid creams. If these help, a milder cream can be used for longer-term control. Antihistamine creams (Zonalon, Pramoxine) or pills (Atarax, Periactin) are often added for additional relief. Intralesional steroid injections, anti-depressant pills, and non-prescription capsaicin cream helps many of those not improved with the usual treatment.
Severe and resistant cases can be controlled with cryotherapy (freezing the sores with liquid nitrogen spray), oral steroids or PUVA. Of course, try not to scratch the spots. In resistant cases blood tests and biopsy of the sores may be needed to look for a cause driving the PN.
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