Diagnostic dilemma: Condition mimics benign disorders
This case illustrates the diagnostic dilemma posed by MF due to its propensity to mimic more benign skin disorders, both clinically and histologically.2 One literature review of MF cases in which the diagnosis was not suspected clinically but was eventually confirmed histopathologically found that 25 unique dermatoses can be mimicked clinically by MF.6 The more common conditions that MF can be mistaken for are discussed below. In light of the diagnostic challenge posed by this multitude of morphologic presentations, referral to Dermatology for histopathologic evaluation is a reasonable next step when empiric treatment fails to improve symptoms of these common skin disorders.
Chronic atopic dermatitis (eczema) is characterized by dry skin and severe pruritis, usually associated with lichenified plaques and a history of atopic disease. The pruritic, scaly plaques typical of MF may be misdiagnosed as eczema; however, a distribution involving the “bathing suit” area is more suggestive of MF. Patients with atopic dermatitis are more likely to display a flexural distribution.2
Tinea corporis typically presents as annular, erythematous, pruritic, scaly patches or plaques that are similar to the scaling lesions of MF. Tinea corporis can be distinguished from MF via potassium hydroxide preparation of skin scrapings from an active lesion, which should demonstrate the segmented hyphae characteristic of this infection. If lesions of this type fail to respond to topical antifungal therapy, a skin biopsy may be warranted for further evaluation.
Nummular eczema, like tinea corporis, presents with round, coin-shaped patches that are highly pruritic and can be difficult to distinguish from the pruritic patches of MF. Unlike MF, however, nummular eczema typically is observed in patients with diffusely dry skin7; the lack of this finding should prompt consideration of alternative diagnoses, including MF.
Psoriasis classically presents with symmetrically distributed, well-demarcated plaques with prominent scaling that are usually asymptomatic, but may be associated with pruritis. Psoriatic plaques may be difficult to distinguish clinically from the plaques of MF, but their distribution may offer clues; psoriasis typically follows an extensor surface distribution, whereas MF is more commonly identified in a “bathing suit” or generalized distribution.4
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