Prurigo nodularis
Overview
Prurigo nodularis (PN) is a skin disease characterised by pruritic (itchy) nodules which usually appear on the arms or legs. Patients often present with multiple excoriated lesions caused by scratching. PN is also known as Hyde prurigo nodularis, Picker nodules, lichen simplex chronicus, atypical nodular form of neurodermatitis circumscripta, lichen corneus obtusus.
Symptoms
* Nodules are discrete, generally symmetric, hyperpigmented or purpuric, and firm. They are greater than 0.5cm in both width and depth (as opposed to papules which are less than 0.5cm). They can appear on any part of the body, but generally begin on the arms and legs. * Excoriated lesions are often flat, umbilicated, or have a crusted top. * Nodules may appear to begin in the hair follicles. * Nodule pattern may be follicular. * In true prurigo nodularis, a nodule forms before any itching begins. Typically, these nodules are extremely pruritic and are alleviated only by steroids.
Causes
The cause of prurigo nodularis is unknown, although other conditions may induce PN. PN has been linked to Becker's nevus, linear IgA disease, an autoimmune condition, and T cells. Systemic pruritus has been linked to cholestasis, thyroid disease, polycythaemia rubra vera, uraemia, Hodgkins disease, HIV and other immunodeficiency diseases. Internal malignancies, liver failure, renal failure, and psychiatric illnesses may induce PN, although more recent research has refuted a psychiatric cause for PN. Patients report an ongoing battle to distinguish themselves from those with psychiatric disorders such as delusions of parasitosis and other psychiatric conditions
Diagnosis
Diagnosis is based on visual examination and the presence of itching. A skin biopsy is often performed to exclude other diseases. Lesion biopsies will typically show a high level of eosinophils in PN. A culture of at least one lesion will rule out staphylococcus infection, which has been significantly linked to atopic dermatitis
Treatment
Prurigo nodularis is very hard to treat, but current therapies include steroids, vitamins, cryosurgery, thalidomide and UVB light. In the event that staphylococcus or other infection is present, antibiotics have proven effective. In at least one case, the root cause of PN was MRSA which was treated with intravenous vancomycin, affecting a complete cure(paper in progress; treat as anecdotal). A physician may administer a strong dose of prednisone, which will almost immediately stop the itch/scratch cycle. However, cessation of steroids allows relapse to occur, usually within a few weeks. Horiuchi et al recently reported significant improvement in PN with antibiotic therapy