Diagnosising Seborrheic Dermatitis

A number of disorders are similar to seborrheic dermatitis. These include:

Atopic dermatitis
Candidiasis
Dermatophytosis
Langerhans cell histiocytosis
Psoriasis
Rosacea
Systemic lupus erythematosus
Tinea infection

One study11 showed that 47 percent of patients with AIDS had recalcitrant eruptions similar to seborrheic dermatitis that may be generalized in children and adults. Highly active antiretroviral therapy may reduce incidence in patients with AIDS.

Psoriasis vulgaris may be difficult to distinguish from seborrheic dermatitis. Psoriasis vulgaris of the scalp presents as sharply demarcated scalp plaques. Other signs of psoriasis, such as nail pitting or distal onycholysis, also may facilitate distinction.

Seborrheic dermatitis also may resemble atopic dermatitis, tinea capitis, and, rarely, cutaneous lymphoma or Langerhans cell histiocytosis. Atopic dermatitis in adults characteristically appears in antecubital and popliteal fossae. Tinea capitis, tinea faciei, and tinea corporis may have hyphae on potassium hydroxide cytologic examination; candidiasis produces pseudohyphae. Seborrheic dermatitis of the groin may resemble dermatophytosis, psoriasis, candidiasis, and, sometimes, Langerhans cell histiocytosis. Rosacea may produce a facial erythema resembling seborrheic dermatitis. Although rosacea tends to include central facial erythema, it may involve only the forehead.

Infants may have atopic dermatitis that is prevalent in certain body areas (e.g., scalp, face, diaper areas, extensor limb surfaces), suggesting seborrheic dermatitis. However, in infants, seborrheic dermatitis has axillary patches, lacks oozing and weeping, and lacks pruritus. The distinction is a clinical one because elevated immunoglobulin E (IgE) levels associated with atopic dermatitis are a nonspecific finding. Rarely, infants are affected by histologic-specific scaling, seborrheic dermatitis-like eruptions on the scalp with fever, and other systemic signs of acute Langerhans cell histiocytosis (Letterer-Siwe disease). Scabetic eczema occasionally resembles widespread seborrheic dermatitis. Riboflavin, biotin, and pyridoxine deficiencies have been associated with seborrheic dermatitis-like eruptions in infants. Concomitant disorders (e.g., psoriasis, scabetic eczema, superficial fungal infection) may complicate seborrheic dermatitis, especially in patients with AIDS.

Skin biopsies may effectively distinguish seborrheic dermatitis from similar disorders. Seborrheic dermatitis should have neutrophils in the scale crust at the margins of follicular ostia. AIDS-associated seborrheic dermatitis more commonly presents as parakeratosis, a few individually necrotic keratinocytes within the epidermis, and plasma cells in the dermis. Yeast cells sometimes are visible within keratinocytes on special stains. If hyphae are present, dermatomycosis is the diagnosis. Shorter hyphae with spores ("spaghetti and meatball pattern") are present with tinea versicolor.