Psoriasis is a chronic skin disorder that has many forms, and various skin disorders may be similar to psoriasis. Thus, it is important to consider the differential diagnosis for psoriasis-like lesions. A definitive diagnosis of psoriasis is made by microscopic examination of a biopsy specimen. Proper diagnosis allows for the most effective treatment.
According to Dr. Johann E. Gudjonsson and Dr. James T. Elder, contributors to “Fitzpatrick’s Dermatology in General Medicine,” psoriasis is a chronic inflammatory skin disease that occurs in 1 to 3 percent of the population. There are generally no symptoms, but some may experience itching that can be severe. Injury or irritation of normal skin sites tends to produce psoriatic lesions at the site. Favored sites include the scalp, elbows, knees, palms, soles and nails. Psoriasis is a lifelong disease characterized by chronic, recurrent exacerbations and remissions that are emotionally and physically debilitating.
Types of Psoriasis
Dr. Thomas P. Habif outlined the various types of psoriasis in “Clinical Dermatology” as follows:
The most common type of psoriasis is the plaque-type. Individuals with plaque-type psoriasis have slowly enlarging plaques. The sites most commonly involved are the elbows, knees, gluteal cleft and the scalp. Skin lesions are often symmetric.
Inverse psoriasis affects the skin folds such as the axilla, groin, submammary region and navel. It may also affect the scalp, palms and soles. The lesions may be moist and not scaly because of their location.
Guttate psoriasis is common in children and young adults. Patients present with many small red, scaling lesions, often following an upper respiratory tract streptococcal infection.
Pustular psoriasis is localized to the palms and soles, or the disease may be generalized. The skin lesions are red pustules that vary in size. Generalized pustular psoriasis is often accompanied by a fever that lasts several days, and it may progress to erythrodermic psoriasis. Pustular psoriasis can be precipitated by local irritants, pregnancy, medications, infections and systemic glucocorticoid withdrawal.
About half of all patients with psoriasis have fingernail involvement, which often manifests as pitting, onycholysis and nail thickening. About 5 to 10 percent of patients with psoriasis have associated joint pain.
According to “Fitzpatrick’s Dermatology,” a diagnosis of psoriasis can be made based on clinical history and physical examination. If history and examination are not diagnostic, biopsy can be used to establish a diagnosis. Characteristics that support a diagnosis of psoriasis include symmetrical lesions, lesions on the posterior aspects of the skin (back of arms, elbows, back of legs), bleeding when the lesions are disturbed, sharp demarcation of lesions and silvery scaled lesions.
"Fitzpatrick’s Dermatology" summarizes treatments for psoriasis in five general categories: topicals, phototherapy, systemics, biologics and combinations of any of these. Topical treatments include steroids, vitamin D analogues, tazarotene, coal tar and calcineurin inhibitors. Phototherapies include UVB light, psoralen and UVA light and laser treatment. Systemic treatments include cyclosporine A, methotrexate, acitretin and fumaric acid esters. Biologic agents modulate activity of the immune system to lessen autoimmune attack that occurs in psoriasis. Such agents include alefacept, efalizumab, etanercept, infliximab and adalimumab.
According to Dr. Gudjonsson and Dr. Elder, the differential diagnosis for plaque psoriasis includes eczema, cutaneous T cell lymphoma, tinea corporis, pityriasis rubra pilaris, seborrheic dermatitis, cutaneous lupus erythematosus, erythrokeratoderma, lichen planus, contact dermatitis, candida infection, Hailey-Hailey disease, squamous cell carcinoma in situ and Bowen disease.
The differential for guttate psoriasis includes pityriasis rosea, pityriasis lichenoides chronic, lichen planus, drug eruption and secondary syphilis.
For pustular and erythrodermic psoriasis, the differential includes drug-induced erythroderma, eczema, cutaneous T cell lymphoma, pityriasis rubra pilaris, impetigo, candida infection, reactive arthritis syndrome, folliculitis, pemphigus foliaceus and IgA pemphigus.