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Therapeutic Strategies

Prurigo Nodularis

Timothy Berger Bruce Wintroub

Saturday, January 01, 2011

Overview

Prurigo nodularis is a morphologic lesion that is a consequence of severe and repeated scratching of one area. In most patients it is secondary to an underlying pruritic condition such as photosensitive dermatitis, renal failure, or neuropathic pruritus due to nerve impingement (brachioradial pruritus). Rarely, bullous pemphigoid may present as prurigo nodularis (pemphigoid nodularis). In some persons, no underlying condition is found. Prurigo nodularis is often very difficult to manage.

Initial Steps

  1. Prescribe high-potency to superpotent topical steroids to be applied 2-4 times daily with or without occlusion.
  2. If there are only a few lesions, intralesional triamcinolone acetonide 5-10 mg/cc to the mid-dermis of the lesion is often of great benefit.
  3. Hydroxyzine or diphenhydramine 25-75 mg before bed and as tolerated 3 times daily.
  4. During the initial visit, an assessment of the patient's mental status is essential. Depression may be present, either as a cofactor in causing the condition, or as a consequence of the chronic, intractable itching.
  5. As a part of the initial evaluation, the cause of the itching should be determined. Dermatitic and neuropathic causes of itching should be sought with appropriate evaluations: skin biopsy; laboratory testing for renal, liver, and endocrine function and anemia; and neurological evaluation for neuropathic pruritus. In some patients, no cause will be detected.
  6. If the lesions are localized to one area, lidocaine impregnated patches 5% may be very effective.

Subsequent Steps

  1. If occlusion with superpotent steroids and/or intralesional therapy fails, consider covering the affected extremities with an occlusive dressing (eg, an Unna boot), changing it weekly every week for 2-4 weeks. If the patient does not remove the dressing or manipulate the lesions beneath it, lesions usually will improve, and after 2-3 weeks the itching will begin to subside in a subset of patients.
  2. If standard antihistamines are of no benefit, antianxiety agents (e.g., alprazolam) or tricyclics (e.g., doxepin) may help. Mirtazapine 25-75 mg nightly may also be an effective antipruritic.
  3. Thalidomide is dramatically beneficial, especially in patients in whom no underlying cause is identified. Since patients are at high risk for the development of neuropathy, begin thalidomide at 50 mg every other day, and increase to 50 mg daily after 6-8 weeks if there has been no response. Most patients respond to doses of 100 mg per day or less. While doses up to 400 mg per day can be used, these high doses dramatically increase the risk of side effects.
  4. Isotretinoin and acitretin in standard acne or psoriasis doses, respectively, may be used as adjunctive treatment in patients with prurigo nodularis.

Pitfalls

  1. Polymorphous light eruption, especially in Native Americans, may appear identical to prurigo nodularis on the extensor surfaces of the upper extremities. Hypertrophic lichen planus, lichen amyloidosis, and discoid lupus erythematosus also may be clinically similar.
  2. Lesions similar to prurigo nodularis can occur in occasional patients with bullous pemphigoid.
  3. Thalidomide is a potent teratogen. It should only be used in otherwise unmanageable patients, by those skilled in its use, and never in women of child-bearing potential.
  4. Thalidomide is associated with the development of sensory neuropathy in up to 45% of patients with prurigo nodularis. The daily dose should be kept at the minimum required. If the maintenance dose is more than 50 mg per day, regular neurological evaluations should be undertaken.
  5. Thalidomide is associated with venous thrombosis and stroke when used in doses above 100 mg per day. Anticoagulation should be considered in these patients.

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