Prurigo nodularis

Published on 18/03/2015 by admin

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Last modified 18/03/2015

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Prurigo nodularis

Christopher Rowland Payne

Evidence Levels:  A Double-blind study  B Clinical trial ≥ 20 subjects  C Clinical trial < 20 subjects  D Series ≥ 5 subjects  E Anecdotal case reports

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Prurigo nodularis (PN) is an excoriated eruption characterized by lichenified nodules. It favors the distal parts of the extensor aspects of the limbs and may be considered a localized form of lichen simplex chronicus.

PN affects all ages and the sex ratio is equal. Pruritus is episodic and disabling. Excoriation is always severe. The eruption is polymorphic. PN has many clinical and histological similarities with eczema. Neural hyperplasia is minimal or absent.

PN usually has an identifiable underlying cause. In half of patients it is due to a cutaneous disorder – usually atopic dermatitis, sometimes gravitational eczema, lichen simplex, nummular eczema, or insect bites, and occasionally subclinical dermatitis herpetiformis or subclinical bullous pemphigoid (known as pemphigoid nodularis). The cause is metabolic in one-third of cases, and in the remainder it is psychological, usually depression, sometimes anxiety or psychosis. The diverse metabolic disorders that cause PN induce itching by a small number of shared mechanisms, most commonly nutritional deficiency, hepatic dysfunction, and uremia, and occasionally thyroid disorder, hypercalcemia, neurological disorder (e.g., stroke), or lymphoma. Nutritional deficiency (the marker of which is reduced iron saturation) usually results from dietary deficiency, such as iron deficiency in women (in which dietary intake is insufficient to compensate for menstrual loss), and sometimes results from malabsorption (more often post-operative than gluten-sensitive) or from gastrointestinal bleeding.

In some patients all three causes (cutaneous, metabolic, and psychological) may be relevant concurrently. Thus, it is not unusual for a particular patient to have more than one underlying drive for itching: for example, PN may be due to atopic dermatitis which has been precipitated and perpetuated by an acute reactive depression and aggravated by concomitant nutritional deficiency (due to the apathetic diet of a lonely person living alone). For a successful outcome in such a patient, the atopic dermatitis, the depression and the diet each need attention. It is not enough just to treat the nodules.

In PN, remission can be expected when there is good patient compliance with symptomatic measures. However, cure is dependent on resolution of the underlying disorder.

Management strategy

The best treatment for PN is holistic. Best therapeutic results are achieved by symptomatic treatment of the cutaneous eruption while concurrently identifying and correcting the underlying cause of the itch. To do this a full medical history, complete physical examination, and a range of simple investigations are needed to determine the driver (or drivers) for the itching, whether metabolic, psychological, or cutaneous.

Symptomatic treatment is very effective. In all patients it is essential to overcome all itching by using full doses of sedating oral antihistamines, such as promethazine 25–75 mg (which is best given 11 hours before rising, rather than at bedtime). Patients may be helped to restrain themselves from excoriation by cutting their nails to the quick, by wearing mittens, or by using occlusive dressings, such as hydrocolloids. Occlusive bandaging or even plaster of Paris casts can be applied in resistant cases. The most potent topical corticosteroids are necessary and should be applied accurately to individual lesions in a cream form or as an impregnated tape (Cordran Tape, Haelan Tape). Intralesional injection of corticosteroids is also helpful (triamcinolone acetonide 40 mg/mL can be injected, 0.1 mL/nodule, and repeated at 6-weekly intervals). Topical capsaicin and/or cryotherapy may be added. When lesions are too numerous to treat topically or by injection, phototherapy with UVB or PUVA may be helpful. In severe and therapy-resistant cases oral thalidomide may be considered.

Treatment of the underlying cause is essential in order to achieve cure. Each specific etiology requires its own specific treatment.

When atopic dermatitis is the cause, treatments aimed at atopic dermatitis are likely to be the most successful. These would include emollients, sedative antihistamines, and potent or very potent topical corticosteroids, sometimes under occlusion.

In PN of metabolic origin, hepatic cases carry the best prognosis: when liver function tests return to normal, a successful outcome can be expected. Nutritional deficiency is common. Although this is often associated with iron deficiency anemia, iron supplements alone are not always helpful. If those deficient of iron are also deficient in other blood-borne nutrients, it is more logical to advise eating 50 g of dark meat daily and 50 g of animal liver each week. Uremia, thyroid disorder, and lymphoma clearly need their own specific treatments.

In patients who scratch for psychological reasons, treatment depends on the underlying disturbance. The most frequent is depression, and this often responds to tricyclic antidepressants, such as dothiepin 75–225 mg nocte or doxepin. Not every case of PN is pruritic, but all are excoriated. Excoriations of marked severity or excoriations without itching may indicate a psychological origin.

First-line therapies

image Sedative antihistamines D
image Occlusion D
image Topical superpotent corticosteroids D
image Topical corticosteroids with occlusion C
image Intralesional corticosteroids E

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