Lichen Simplex Chronicus –salient features

·        A chronic, severely pruritic disorder characterized by one or more lichenified plaques. ·        Most common sites of involvement are scalp, nape of neck, extensor aspects of extremities, ankles, and anogenital area. ·        Pathology consists of hyperkeratosis, hypergranulosis, psoriasiform epidermal hyperplasia, and thickened papillary dermal collagen.

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PrurigoNodularis-salient features

·        A pruritic disorder that runs a chronic course. ·        Hyperkeratotic firm nodules vary in size from 0.5 to 3 cm and may be excoriated. ·        Associations include atopic dermatitis, or systemic causes of pruritus. ·        Pathology consists of hyperkeratosis, hypergranulosis, psoriasiform epidermal hyperplasia, thickened papillary dermal collagen, and characteristic neural hypertrophy.

 

Introduction

 

Lichen simplex is an eczematous dermatosis characterized by epidermal hypertrophy that results from chronic, habitual rubbing or scratching localized areas of skin. Lichenification is a change in appearance and texture of the skin associated particularly with pruritic dermatoses.  Lesions of LSC itch spontaneously, leading to an “itch–rub–itch” cycle. Lichenification may occur spontaneously, when it is known as lichen simplex, or may occur as a secondary consequence of eczema and other inflammatory dermatoses. The lichenified skin is like an erogenous zone as it becomes a pleasure (orgiastic) to scratch. The rubbing becomes automatic and reflexive, like an unconscious habit.

PN can be defined as a highly pruritic condition with numerous, symmetrically distributed, hyperkeratotic or eroded nodules. The lesions of prurigo nodularis are produced by chronic, repetitive, focused scratching or picking of the skin. The nodules themselves are also intensely pruritic, possibly due to hypertrophy and increased density of substance P-positive nerves within affected skin, leading to perpetuation of the itch–scratch cycle.

 

Epidemiology

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Lichen simplex chronicus affects adults, predominantly from ages 30 to 50. Females are affected more commonly than males. Prurigo nodularis may occur at any age, but most patients are between 20 and 60 years. Men and women are equally affected. Patients with coexistent atopic dermatitis have been found to have any earlier age of onset (mean: 19 years) as compared to the nonatopic group (mean: 48 years).

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Etiology and Pathogenesis

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Lichen simplex chronicus is induced by rubbing and scratching secondary to itch. The prurigo nodule is induced by picking and scratching most commonly in response to itch. Both types of lesions are commonly found in patients with atopic dermatitis along with xerosis and other signs and symptoms of atopic dermatitis. In the nonatopic LSC and PN group, systemic causes of pruritus, including renal insufficiency, hyper- or hypothyroidism, liver failure, HIV disease, parasitic infection, or an underlying malignancy must be excluded. Hepatitis B and C have been reported as associations without liver failure. LSC may develop superimposed on other dermatosis, including contact dermatitis, psoriasis, candidiasis and tinea infections. PN may also occur in other dermatosis, such as contact dermatitis and pemphigoid nodularis, a rare variant of BP. Both prurigo nodularis and lichen simplex chronicus are associated with emotional or psychological factors including Obsessive-compulsive disorder (OCD).

 

 

Clinical features

 

History

 

++Severe itching is the hallmark of LSC and PN and is often out of proportion to the extent of the objective changes.  Itching may be paroxysmal or continuous. Scratching tends to give initial satisfaction, and may be conscious and to the point of replacing the sensation of itch with pain, or may be unconscious, occurring during sleep. Itch is often triggered by sweating, heat, extreme humidity or irritation from personal care products or clothing and/or at times of psychological distress.

 

Presentation

 

In lichen simplex, usually, only one plaque is present; however, more than one site may be involved.  Almost any area may be affected, but the commonest sites are those that are conveniently reached. The usual sites are the occipital scalp, nape of the neck (especially in women), anogenital region (labia majora in women and the scrotum in men), lower legs and ankles, upper thighs, and dorsal aspects of the hands, feet, and forearms.

 

A solid plaque of lichenification, that arises from the confluence of small papules. Skin is palpably thickened; skin markings (barely visible in normal skin) are accentuated and can be readily seen giving a “leathery” appearance along with hyper pigmentation, and varying degrees of erythema. The lesions are excoriated and are usually sharply defined. There may be isolated single lesion or several plaques. Lesions of LSC are broader and thinner than those of prurigo nodularis. In dark skin tones, lichenification may assume a special type of pattern consisting of multiple small (2 to 3 mm) closely set papules, a "follicular" pattern.  LSC can last for decades unless the rubbing and scratching are stopped by treatment.

The typical lesion of PN is firm, dome-shaped nodules that develop on sites in which persistent itching and scratching occur. Nodules are often eroded, excoriated, and sometimes even ulcerated as patients dig into them with their nails. The color ranges from skin-toned to erythematous to brown, and hyperpigmentation is particularly common in dark-skinned individuals. Lesions can develop a verrucous or fissured surface, and lichenification of adjacent skin may be observed. When crusts, but not clear-cut papulonodular lesions, are present, the term prurigo simplex is sometimes utilized. The nodules may be roundish or flat and large (plaques). In some patients, the PN lesion starts as a papule and then develops into a nodule.

Multiple lesions disseminated bilaterally and symmetrically over the whole skin but preferentially on the extensor aspects of the limbs, the upper back, lumbosacral area and buttocks; but the difficult-to-reach mid upper back is classically spared (“butterfly sign”). Flexural areas, the face, and the groin are usually not affected; however, nodules may occur on any site that can be reached by the patient. Lesions may vary in number from few to more than one hundred. Nodules resolve with post inflammatory hyper- or hypopigmentation with scarring.

 

Related Physical Findings

 

++In patients with atopic eczema, the intervening skin is often lichenified and xerotic and patients may have other signs of atopy such as Dennie-Morgan fold or palmar hyperlinierity. In nonatopic patients, cutaneous signs of underlying systemic disease or lymphadenopathy, signifying lymphoma, may be present.

 

 

Laboratory Tests

 

++In patients with LSC and PN 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. HIV 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.

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Special Tests

 

++On histopathologic sections, both LSC and PN consist of compact hyperkeratosis, psoriasiform epidermal hyperplasia, hypergranulosis, and thickened vertically arranged collagen bundles in the papillary dermis.

 

Possibly as a result of intense scratching, prurigo nodularis lesions demonstrate hypertrophy and an increased density of dermal nerve fibers. Although only occasionally evident with routine staining, this can be highlighted by immunostaining for a pan-neuronal marker such as protein-gene product 9.5 (PGP-9.5). In contrast, the number of nerve fibers within the epidermis is reduced. There is increased expression of substance P, CGRP, and NGF receptors by the dermal nerve fibers and prominent NGF immunoreactivity in lesional dermis. The dermal neuronal hyperplasia and epidermal “small fiber neuropathy” may play a pathogenic role in perpetuating the pruritus of prurigo nodularis.

 

 

Prognosis/Clinical Course

 

++Both diseases run a chronic course with persistence or recurrence of lesions unless the itch–scratch cycle can be broken. Exacerbations occur in response to emotional stress.

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Treatment

 

++Treatment is aimed at interrupting the itch–scratch cycle. Both components should be addressed. Ideally, significantly reducing the pruritus would break the itch–scratch cycle, eventually leading to healing of the lesions; however, this is often not possible, especially when there is a psychological underpinning. Systemic causes of itch should be identified and addressed. In both conditions, first-line measures to control itch include potent topical steroids as well as nonsteroidal antipruritic preparations such as menthol, phenol, pramoxine, polidocanol or palmitoyl ethanolamine 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. Topical tacrolimus has been successfully employed as a steroid-sparing agent. Sedating antihistamines, such as hydroxyzine 25 to 5O mg at night, may be used to abolish night time itch in both conditions. Patients with conventional therapy-resistant PN found that daily 10 mg motelukast and 240mg fexofenadine twice daily may help in reducing itch in 75% of patients. Selective serotonin reuptake inhibitors (SSRIs) have been recommended for relief of daytime pruritus or in patients with OCD. 

 

++Capsaicin, calcipotriene, and cryotherapy have all been successfully used in prurigo nodularis. Both broad- and narrow-band ultraviolet B, as well as topical or oral PUVA show efficacy and are indicated in widespread cases. The 308 nm excimer monochromatic light, UVA1 phototherapy, and naltrexone are all found to be effective.  In severe cases, gabapentin 300 mg po tid and pregabalin 25 mg orally tid are thought to improve itching by inhibiting excitatory neurotransmitters through calcium inhibition. Patients should be revaluated after three months and dosages lowered for maintenance. Oral cyclosporine (3 to 5 mg/kg daily) has also been shown to be beneficial.

 

For the most recalcitrant patients, thalidomide and lenalidomide may be effective. 

++The importance of avoiding scratching should be addressed with the patient. Nails should be kept short and occlusive measures, such as plastic films, in refractory cases may be needed.

 

 

 

 

 

 

 

 

 

 

 

 

 

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