Prurigo Nodularis

 

·         Described by Hyde in 1909; also known as nodular prurigo.

·         A pruritic disorder that runs a chronic course.

·         Hyperkeratotic, firm nodules vary in size from 0.5 to 3.0 cm and may be excoriated.

·         Associations include atopic dermatitis or systemic causes of pruritus.

·         Pathology consists of hyperkeratosis, hypergranulosis, and psoriasiform epidermal hyperplasia. Dermal changes include thickened papillary dermal collagen and characteristic neural hyperplasia.

Prurigo nodules vary in size from 0.5 to 3.0 cm and are firm to hard on palpation. The surface may be hyperkeratotic or crateriform. There is often overlying

excoriation. Pruritus is usually severe. Limbs are affected in most cases, especially the extensor aspects . The abdomen and sacrum were the next most common sites of involvement in one study. Face and palms are rarely involved; however, nodules may occur on any site that can be reached by the patient. Lesions may vary in number from few to more than 100. Nodules resolve with post-inflammatory hyper- or hypopigmentation with or without scarring.

 

RELATED PHYSICAL FINDINGS

In patients with atopic eczema, the intervening skin is often lichenified and xerotic. In non-atopic patients, cutaneous signs of underlying systemic disease or lymphadenopathy, signifying lymphoma, may be present.

 

Laboratory Tests

In patients with prurigo nodularis in whom an underlying systemic cause of pruritus is suspected, a complete blood count with differential count, renal, liver, and thyroid function tests may be ordered. A chest x-ray may be obtained to screen for lymphoma. Human immunodeficiency virus testing may also be indicated. The need for a more extensive evaluation may be individualized based on patient history and results of the aforementioned tests.

 

Special Tests

On histopathologic sections, lichen simplex chronicus shows varying degrees of hyperkeratosis with para- and orthokeratosis, hypergranulosis, and psoriasiform epidermal hyperplasia. The papillary dermis shows thickening of collagen with coarse collagen bundles and vertical streaks. There is a variable inflammatory infiltrate around the superficial vascular plexus with lymphocytes, histiocytes, and eosinophils. A biopsy may also reveal a primary pruritic disorder that has led to secondary lichenification, such as psoriasis.

The epidermal findings in prurigo nodularis are similar to lichen simplex chronicus. The lesion is more papular with bulbous epidermal hyperplasia. Papillary dermal changes also resemble lichen simplex chronicus. There is cutaneous neural hyperplasia with thickened nerve bundles and an increase in nerve fibers by S-100 staining. This is not seen in other pruritic disorders, including lichen simplex chronicus.

 

Complications

Sleep studies have shown that disturbances in the sleep cycle in patients with lichen simplex chronicus are present. Non-rapid eye movement sleep is disturbed, and patients have an increased arousal index (brief awakenings from sleep) caused by scratching.

 

Differential Diagnosis of Lichen Simplex Chronicus

Most Likely

·         Lichenified atopic eczema

·         Lichenified psoriasis

·         Hypertrophic lichen planus

Consider

·         Genital: Extramammary Paget disease

Always Rule Out

·         Vulva, perianally: Underlying lichen sclerosus, HPV, or tinea cruris

·         Scrotum: Underlying HPV or tinea cruris

HPV = human papillomavirus.

Prognosis and Clinical Course

Both diseases run a chronic course with persistence or recurrence of lesions. Exacerbations may occur in response to emotional stress.

Treatment

Treatment is aimed at interrupting the itch-scratch cycle. Both components should be addressed. Systemic causes of itch should be identified and addressed. In both conditions, first-line measures to control itch include potent topical steroids, best under occlusion, as well as nonsteroidal antipruritic preparations such as menthol, phenol, or pramoxine. Emollients are an important adjunct. Intralesional steroids, such as triamcinolone acetonide, given in varying concentrations according to the thickness of the plaque or nodule, are beneficial. Sedating antihistamines, such as hydroxyzine, or tricyclic antidepressants, such as doxepin, may be used to abolish nighttime itch in both conditions. Selective serotonin reuptake inhibitors have

been recommended for relief of daytime pruritus or in patients with obsessive-compulsive disorder.¹⁶

 

Differential Diagnosis of Prurigo Nodularis

Most Likely

·         Perforating disease

·         Hypertrophic lichen planus

·         Pemphigoid nodularis

·         Actinic prurigo

·         Multiple keratoacanthomas

Consider

·         Nodular scabies

·         Dermatitis herpetiformis

Capsaicin, calcipotriene, topical tacrolimus, and cryotherapy, with or without intralesional steroid injections, have all been successfully used in prurigo nodularis. Both broad- and narrowband ultraviolet B, as well as topical or oral psoralen and ultraviolet A light, show efficacy and are indicated in widespread cases. Thalidomide and cyclosporine have also been shown to be beneficial. Naltrexone has shown efficacy in a small series.

The importance of avoiding scratching should be addressed with the patient. Nails should be kept short and occlusive measures, such as plastic films, topical steroid tape, or Unna boots in widespread cases, may be needed.