Prurigo Nodularis Clinical Presentation
- Author: Daniel J Hogan, MD; Chief Editor: Dirk M Elston, MD more...
History
Prurigo nodularis patients are most often middle-aged to elderly. Patients with prurigo nodularis invariably complain of a long-standing history of severe, unremitting pruritus. Patients can point out specific sites where they began feeling itchy and where dark-colored nodules formed soon after. Mature nodules rarely increase or decrease in size; spontaneous resolution is even more rare. Prurigo nodularis is usually bilaterally symmetric, with nodules that are either stable or increasing in number.
The patient's medical history may be significant for several conditions, as follows:
- Hepatic or renal dysfunction
- Local trauma or insult to the skin
- Infection
- HIV/immunodeficiency[2]
- Anxiety or other psychiatric condition
Patients may have no significant medical or psychiatric history. The patient's history often reveals a long list of over-the-counter and/or prescribed medications (topical and oral), which usually have produced little or no relief of symptoms. Up to 80% of patients have a personal or family history of atopic dermatitis, asthma, or hay fever (compared with approximately 25% of the normal population).
Physical
Prurigo nodularis nodules or papules are 3-20 mm in diameter; they are discrete, scaly, generally symmetric, hyperpigmented or purpuric, and firm. Nodules and papules occur on the extensor surfaces of the arms, the legs, and sometimes the trunk.
Prurigo nodularis lesions may show signs of excoriation with flat, umbilicated, or crusted top. Lesions may number from 1-2 to hundreds. The nodule pattern may be follicular. Upon entering the examination room and while patients' describe the locations of the lesions, patients may scratch or rub the lesions rather than pointing to them. Many prurigo nodularis patients appear very anxious, worried, or even obsessed with the nodules. Note the images below.
Prurigo nodularis. Courtesy of Jeffrey Meffert, MD.
Prurigo nodularis. Courtesy of Jeffrey Meffert, MD. Causes
The cause of prurigo nodularis is still unknown. Many associated conditions are known, but their roles as coexisting or preexisting conditions have not been established in causing prurigo nodularis. 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 prurigo nodularis; 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.[3] They are both found in increased numbers in prurigo nodularis. 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.
Calcitonin gene–related peptide and substance P immunoreactive nerves are markedly increased in prurigo nodularis skin compared with normal skin.[4] These neuropeptides may mediate the cutaneous neurogenic inflammation and pruritus in prurigo nodularis. 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 prurigo nodularis lesions, but these can be normalized with capsaicin application.
Hepatitis C, mycobacteria,[5, 6, 7]Helicobacter pylori, Strongyloides stercoralis,[8] and HIV have been reported as infectious etiologies of prurigo nodularis or as associated with prurigo nodularis 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 prurigo nodularis.[9] Interleukin 31 expression in atopic individuals is also rapidly induced by staphylococcal superantigen; however, the link between these findings has not been extensively researched.
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