[url=javascript:MakeImageWindow('http://www.aocd.org/images_ddd/prurigo_nodularis_1.jpg','prurigo%20nodularis',250,385)][/url]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.
[url=javascript:MakeImageWindow('http://www.aocd.org/images_ddd/prurigo_nodularis_2.jpg','prurigo%20nodularis',385,250)][/url]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 Zostrix 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.
The cause of PN (Prurigo nodularis) is still unknown. Many associated conditions are known, but their roles as coexisting or preexisting conditions have not been established in causing PN. Notable changes in papules and nodules are increased in certain inflammatory cell types, inflammatory products, and neural hyperplasia.
Mast cells and neutrophils are seen in higher-than-normal levels in PN; however, their degranulation products are not increased. Eosinophils are not seen in higher numbers; however, the protein granule products (ie, major basic protein, eosinophil cationic protein, eosinophil-derived neurotoxin) are seen in significantly higher levels.
Papillary dermal nerves and Merkel cells are sensory nerves found in the dermis and the epidermis, respectively. They are both found in increased numbers in PN. These are neural receptors that sense touch, temperature, pain, and itch. These increases in sensory nerves are not seen in lichen simplex chronicus, another pruritic disease that causes epidermal hyperplasia but in a plaquelike morphology (see Lichen Simplex Chronicus).
Calcitonin gene–related peptide and substance P immunoreactive nerves are markedly increased in PN skin compared with normal skin. These neuropeptides may mediate the cutaneous neurogenic inflammation and pruritus in PN. In addition, the capsaicin-binding nonselective cation channel known as vanilloid receptor subtype 1 has highly increased expression in epidermal keratinocytes and nerve fibers in PN lesions, but these can be normalized with capsaicin application.
Hepatitis C, mycobacteria, Helicobacter pylori, Strongyloides stercoralis, and HIV have been reported as infectious etiologies of PN or as associated with PN in case reports or from single-center studies.
Interleukin 31, a T-cell–derived cytokine that causes severe pruritus and dermatitis in transgenic mice, is elevated in individuals with PN. Interleukin 31 expression in atopic individuals is also rapidly induced by staphylococcal superantigen; however, the link between these findings has not been extensively researched.
Medical Care
Current available treatments of PN have had mild-to-moderate success at best. Often, combinations of several medications or physical modalities may be used in an attempt to control this process.
Topical, oral, and intralesional corticosteroids have all been used in attempts to decrease inflammation and sense of itching and to soften and smooth out firm nodules. The improvement with corticosteroids is variable, and corticosteroids are sometimes not helpful.
Menthol, phenol, pramoxine, capsaicin cream, vitamin D-3 ointment, and topical anesthetics are some other topical agents used to reduce pruritus. Treatment with DuoDerm or other occlusive therapies has been suggested to flatten lesions while at the same time preventing patients from directly scratching nodules.
UV light treatment using UV-B or UV-A plus psoralen may be beneficial for severe pruritus. Consider the adverse effects of prolonged UV exposure before such treatment.
Antihistamines, anxiolytics, opiate receptor antagonists, and (most recently) thalidomide are oral medications other than steroids used for PN. Thalidomide has been shown to aid in several severe dermatoses, including PN with or without associated HIV disease. Severe teratogenic effects are well known and documented, and all women of childbearing age should be on adequate birth control methods. Patients taking thalidomide have an increased risk of peripheral neuropathy.
Surgical Care
Cryotherapy with liquid nitrogen helps reduce pruritus and flatten lesions.
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Thirty-second thaw cycles with 2-4 treatments are recommended, depending on the size of the lesion.
Understanding the risks of scarring and change in pigmentation (especially in darker-skinned individuals) is important.
Cryotherapy may be combined with other modalities (eg, intralesional corticosteroids).
Pulsed dye laser therapy may help reduce the vascularity of individual lesions.