Differential Diagnosis
The differential diagnosis for axillary lesions is broad, including infectious, inflammatory, and autoimmune etiologies. Irritant contact dermatitis (ICD) presents similar to ACD, though it is more immediate in onsetand typically demonstrates symptoms of burning and stinging rather than pruritus. Although histopathology is not reliable in differentiating ICD and ACD, it has been shown that focal parakeratosis is associated with ACD, whereas necrotic epidermal keratinocytes are found in ICD.100
Intertrigo presents as large, erythematous, opposing patches or plaques confined to inguinal, submammary, axillary, and/or abdominal folds. Findings of beefy red erythema and peripheral satellite pustules may implicate presence of Candida, which can be identified with potassium hydroxide preparations.
Inverse psoriasis presents as sharply demarcated, erythematous, moist, smooth plaques or patches with minimal scale. The most common area of involvement is the inguinal folds, followed by the axillae, inframammary folds, perianal area, umbilicus, and retroauricular areas. Involvement of the elbows and knees or a positive family history of psoriasis may be useful knowledge in establishing the diagnosis. A biopsy may show dermal eosinophils, epidermal spongiosis, and focal serum in the scale, in addition to features of typical psoriasis plaques.101
Seborrheic dermatitis typically is an erythematous eruption, often with yellowish greasy scale. Simultaneous involvement of the face and scalp may be noted. Although typically a clinical diagnosis, biopsy demonstrates shoulder parakeratosis with follicular plugging and lymphocytic exocytosis.
Hailey-Hailey disease (also called benign familial pemphigus) is an autosomal-dominant genetic condition presenting as moist, malodorous, painful, vegetative plaques, patches, or scaly pustules in flexural areas, frequently with flaccid blisters. Lesions are provoked by traumatic stimuli. Onset occurs in the second to fourth decades and may improve with age. The diagnosis is confirmed by biopsy, which demonstrates acantholysis of the epidermis. The moist superficial patches of Hailey-Hailey disease help distinguish it from comparably drier Darier disease, the other acantholytic disease of the axillae.
Granular parakeratosis (also called hyperkeratotic flexural erythema) is an uncommon dermatosis most often observed in middle-aged women. It presents as red-brown keratotic papules coalescing into plaques, often with overlying scale in intertriginous areas. This disorder may be related to exposure to aluminum, a key component of antiperspirants.102 Diagnosis with a skin biopsy demonstrates granular parakeratosis.
Infections most commonly include erythrasma, tinea, and candidiasis. Erythrasma caused by Corynebacterium minutissimum may present in the axillae and/or groin with sharply demarcated, red-brown patches. Wood lamp examination reveals coral red fluorescence. Tinea corporis, a dermatophyte infection, may present as scaly erythematous plaques with advancing borders and central clearing. Fungal cultures and potassium hydroxide preparations are useful to confirm the diagnosis.