Papulosquamous skin eruptions

Papulosquamous skin disorders are inflammatory reactions characterized by red or purple papules and plaques with scale. These diseases include psoriasis, pityriasis rubra pilaris, seborrheic dermatitis, pityriasis rosea, pityriasis lichenoides et varioliformis acuta, and parapsoriasis. Lichen planus and lichen nitidus are also considered papulosquamous disorders (see Chapter 12).

Habif TP: Clinical dermatology: a color guide to diagnosis and therapy, ed 4, St Louis, 2004, Mosby.

Psoriasis is a common, genetically determined, inflammatory, and hyperproliferative skin disease. Although there are morphologic variations, the most characteristic lesions consist of chronic, well-demarcated, dull-red plaques (Fig. 7-1A) with silvery scale found commonly on extensor surfaces and the scalp (Fig. 7-1B).

The different clinical presentations of psoriasis can be separated by morphology or location.

Morphologic variants	Locational variants
Chronic plaque psoriasis	Scalp psoriasis
Guttate psoriasis	Palmoplantar psoriasis
Pustular psoriasis	Inverse psoriasis
Erythrodermic psoriasis	Nail psoriasis
Psoriatic arthritis

Guttate psoriasis is a variant of psoriasis usually seen in adolescents and young adults. It is characterized by crops of small, droplike, psoriatic papules and plaques (Fig. 7-2A). The word guttate is derived from the Latin gutta, which means “drop.” This type of psoriasis is often found in association with streptococcal pharyngitis, and treatment of the pharyngitis with oral antibiotics may improve or even clear the psoriasis.

Inverse psoriasis refers to psoriasis that involves intertriginous areas (axillae, groin, umbilicus). This distribution is opposite to the usual extensor distribution of psoriasis vulgaris. Psoriatic lesions with both distributions sometimes can be found in the same patients. Clinically, psoriatic lesions found in these “inverse” distributions often do not have scale, but consist of sharply demarcated red plaques that may become macerated and eroded (Fig. 7-2B). Treatment of inverse psoriasis usually involves low-potency (nonfluorinated) topical corticosteroids.

Although a specific genetic abnormality has not been identified, psoriasis is generally considered to be a genetically determined disease. There are reports of striking family pedigrees that suggest an autosomal dominant inheritance, but with only partial penetrance. Keep in mind that psoriasis is probably not a single disease, but a family of diseases involving epidermal hyperproliferation. The external environment presumably plays a role in the clinical expression. The strongest evidence for the importance of external factors in the expression of psoriasis is seen in acute guttate psoriasis, which often occurs in association with streptococcal pharyngitis.

Travers JB, Hamid QA, Norris DA, et al: The environment of psoriasis allows enhanced reactivity to epicutaneously applied bacterial exotoxins, J Clin Invest 104:1181–1189, 1999.

Although the exact incidence of psoriatic arthritis is unknown, an estimated 5% to 10% of patients with psoriasis suffer from psoriatic arthritis. The arthritis may precede, accompany, or, more commonly, follow the development of the skin disease. The five types of psoriatic arthritis are

Asymmetrical arthritis, the most common form of psoriatic arthritis, usually involves one or several joints of the fingers or toes. The appearance of this type of arthritis can be similar to subacute gout and include “sausage-like” swelling of a digit due to involvement of the proximal and DIP joints and the flexor sheath (Fig. 7-3). Symmetrical polyarthritis resembles rheumatoid arthritis, but tests for rheumatoid factor are negative, and the condition is clinically less severe than rheumatoid arthritis. Although not common, DIP joint disease of hands and feet is the most classic presentation of arthritis with psoriasis. Destructive arthritis (arthritis mutilans) is a rare, severely deforming arthritis involving predominantly fingers and toes. Gross osteolysis of the small bones of the hands and feet can result in shortening, subluxations, and, in severe cases, telescoping of the digits, resulting in an “opera glass” deformity. Axial arthritis of the spine, which resembles idiopathic ankylosing spondylitis, manifests by itself or with peripheral joint disease.

A careful examination of the nails should be part of the skin exam, especially when evaluating a rash that might be psoriasis. Characteristic nail changes are found in 25% to 50% of psoriatics. These changes include nail pitting, discoloration, onycholysis, subungual hyperkeratosis, and nail deformity. Nail pitting, the most common nail finding in psoriasis, consists of small, discrete, punched-out depressions on the nail surface (Fig. 7-4). Circular areas of nail bed discoloration that resemble oil drops are often seen under the nail plate (hyponychium). The nail can become thin and brittle at the distal edge with separation from the nail bed (onycholysis) or thickened with subungual debris. Ridges, grooves, or even frank deformity of the nail plate can also be seen.

The isomorphic or Koebner phenomenon is the development of a cutaneous eruption at the site of physical trauma (scratch, surgical wound, or sunburn). Other skin conditions that exhibit the Koebner phenomenon include lichen planus, lichen nitidus, and vitiligo. Patients with psoriasis should be warned of this tendency before subjecting themselves to cosmetic procedures involving physical trauma (such as having a tattoo).

The Auspitz sign is the presence of small bleeding points seen on a psoriatic lesion when the scales are removed. This bleeding is due to thinning of the epidermis between the elongated rete ridges. Note that it is not a good idea to attempt to elicit these two signs on your psoriatic patients.

Patients with limited disease (usually <20% of their body surface) can often be managed on topical agents alone. Although systemic corticosteroids generally should not be used, topical and intralesional corticosteroids are a first-line treatment. For plaques, medium- to high-potency corticosteroids used daily can result in a rapid response, often controlling the inflammation and itching. Unfortunately, the relief is often temporary, and tolerance can occur. Side effects include atrophy and telangiectasias, especially if high-potency topical preparations are used on the face or intertriginous areas (see also Chapter 54).

Coal tar preparations can also be effective, especially if used with topical corticosteroids. Anthralin, a synthetic derivative of chrysarobin, a tree bark extract, is effective in daily, short applications for chronic plaque psoriasis, but its irritant qualities often worsen inflammatory psoriasis. Calcipotriene (Dovonex), a vitamin D3 analog, is an effective treatment for localized psoriasis, but its cost and the possibility of systemic absorption resulting in changes in calcium homeostasis preclude its use in extensive disease. Calcipotriene should be limited to a maximum dosage of 100 gm/wk. A newer and potentially more effective treatment is the combination of calcipotriene and the corticosteroid, betamethasone diproprionate (Taclonex).

Menter A, Gottlieb A, Feldman SR, et al: Guidelines of care for the management of psoriasis and psoriatic arthritis. Section 1. Overview of psoriasis and guidelines of care for the treatment of psoriasis with biologics, J Am Acad Dermatol 58:826–850, 2008.

It has been known for centuries that sunlight exposure can improve psoriasis. Two forms of ultraviolet radiation are used clinically: ultraviolet B (UVB, 290 to 320 nm) and ultraviolet A (UVA, 320 to 400 nm) combined with an oral photosensitizer, psoralen plus UVA (PUVA). Although not as effective as PUVA, use of UVB results in less incidence of side effects and is often used first in the treatment of light-sensitive psoriasis (see also Chapter 54).

Methotrexate, cyclosporine, and retinoids (i.e., acitretin). Because of the potential side effects of these agents, their use should be carefully considered by the physician and patient. Methotrexate suppresses DNA synthesis by inhibiting the enzyme dihydrofolate reductase. In addition to its antimitotic effects, methotrexate inhibits neutrophil function. Side effects include bone marrow suppression, stomach upset, and hepatotoxicity. Although the incidence of hepatic fibrosis and cirrhosis is low with cumulative doses <1.5 gm, liver function tests are not a reliable indicator of methotrexate-induced hepatotoxicity, and a liver biopsy is recommended after 1.5 gm and every 1.0 to 1.5 gm thereafter. Methotrexate should be avoided in psoriatic patients who have underlying liver disease, renal disease, or are heavy drinkers. Patients who take methotrexate should be aware of its interactions with many other medications.

The antilymphocytic drug cyclosporine can be used for severe psoriasis. It has a relatively rapid onset of action, but side effects such as hypertension and nephrotoxicity limit its use as a long-term agent. The doses used, 3 to 5 mg/kg/day, are usually lower than the dosages used to inhibit organ transplant rejection.

Systemic retinoids such as acitretin are first-line agents in pustular psoriasis and also may be used to treat chronic plaque psoriasis. Unlike methotrexate and cyclosporine, retinoids do not suppress the immune system. Rather, retinoids likely mitigate the epidermal hyperproliferation seen in psoriasis. Acitretin is a potent teratogen and must be avoided in women of child-bearing age. Other systemic treatments include the “biologicals,” which will be covered in the next question.

Biologic agents are proteins derived from living cells that are used to modulate specific portions of the aberrant immune response that leads to psoriasis. They are administered by subcutaneous, intramuscular, or intravenous injection. Tumor necrosis factor (TNF) alpha inhibitors (etanercept, adalimumab, and infliximab), as well as alefacept, are used in the treatment of refractory or extensive psoriasis. The TNF-α inhibitors block the proinflammatory action of TNF-α, a potent cytokine that mediates the formation of psoriatic plaques. Risks of TNF-α inhibitors include increased susceptibility to infections, such as reactivation of tuberculosis or hepatitis B, and higher rates of malignancy such as lymphoma.

Alefacept binds to and inhibits memory T lymphocytes that express CD2, which reduces the number of these pathogenic T cells. Patients undergoing alefacept therapy must be monitored for lymphopenia. Alefacept is less effective than the TNF-α inhibitors and is rarely used in clinical practice.

The newest biologic agent (FDA-approved in September, 2009) is ustekinumab, a humanized antibody against the p40 subunit found in the cytokines interleukin (IL)-12 and IL-23. In particular, the inhibition of IL-23 blocks the T-cell pathway (TH17) recently implicated in the pathogenesis of psoriasis.

Although these systemic psoriasis therapies may be more effective, care must be exercised in their use, especially because the long-term side effects of biological agents are not completely clear.

Pityriasis rubra pilaris (PRP) is a rare disease in which the primary abnormality appears to be hyperproliferation of the epidermis (Fig. 7-5). Five variants have been described, the most common being type I, the classic adult-onset form. In this type, the eruption commonly begins on the head and neck as reddish-orange, slightly scaly macules and thin plaques. The rash extends in a cephalocaudal fashion, and within several weeks, red, perifollicular papules with central plugs develop in the lesions. The scalp often develops extensive yellowish scale. The palms and soles become thickened and yellow, which is called keratoderma. This results in a well-demarcated, very characteristic “PRP sandal.” Although total body involvement (erythroderma) is not uncommon, the rash of PRP often has characteristic skip areas of normal skin (“islands of sparing”). Considering that the rash usually looks very impressive, it is surprising that patients often complain of only mild irritation and pruritus.

Treatment strategies for PRP depend on the extent of involvement and how much the patient is bothered. Lubrication with emollients and topical corticosteroids are rarely helpful. The treatment of choice is oral retinoids, with methotrexate being reserved for retinoid-resistant cases.

Seborrheic dermatitis is a chronic dermatitis with a typical morphologic appearance of red plaques with greasy yellow scales, distributed in the seborrheic areas. Scalp involvement is almost universal. Facial involvement is common and manifests itself as erythema and scaling on the medial sides of the eyebrows, glabella, and nasolabial folds. Ocular involvement (blepharitis and conjunctivitis) and ear involvement (external auditory canal and posterior auricular scalp) are also frequently seen. Visible scalp desquamation, commonly known as dandruff, is probably the precursor and/or a mild form of seborrheic dermatitis.

Naldi L, Rebora A: Clinical practice. Seborrheic dermatitis, N Engl J Med 360:387–396, 2009.

Pityriasis rosea is an acute, benign, self-limiting disorder that affects teenagers and young adults. The eruption has a characteristic pattern, and three fourths of cases start with a single 2- to 4-cm, sharply defined, thin, oval plaque. Within a few days to weeks, crops of similar-appearing, though usually smaller, papules follow the initial “herald patch” (Fig. 7-6). The eruption characteristically involves the trunk and proximal extremities, usually sparing the face, palms, and soles. Lesions on the trunk tend to run parallel to the lines of skin cleavage, resulting in a “Christmas tree” pattern. The lesions usually resolve within several weeks to a month but may persist longer. Except for a mild prodrome, affected patients are usually asymptomatic. The lesions of pityriasis rosea often have “trailing scale” (e.g., collarette of scale that does not extend to the border of the lesion), and papular variants can be seen, especially in children.

Drago F, Broccolo F, Rebora, A : Pityriasis rosea: an update with a critical appraisal of its possible herpesviral etiology, J Am Acad Dermatol 61:303–318, 2009.

Pityriasis lichenoides et varioliformis acuta (PLEVA or Mucha-Habermann disease) is a rare disease characterized by crops of polymorphous lesions on the trunk, thighs, and upper arms. The eruption consists of red-brown papules that can become purpuric, scaly, and even necrotic (Fig. 7-7). The patients usually are asymptomatic, although itching and low-grade fevers and malaise are not uncommon. Individual lesions resolve in several weeks leaving postinflammatory hyper- or hypopigmentation and occasionally scars. The clinical course of PLEVA often waxes and wanes and can last months to years.

Khachemoune A, Blyumin ML: Pityriasis lichenoides: pathophysiology, classification, and treatment, Am J Clin Dermatol 8:29–36, 2007.