Case Presentation: A 66-year-old man with atopic dermatitis (managed with topical triamcinolone) presented with three weeks of a diffuse pruritic eczematous rash, anorexia, and a 15-lb weight loss. Vital signs were normal, but he was cachectic (BMI 15) with palpable inguinal lymphadenopathy and erythroderma affecting over 90% of his body. He was admitted for inability to care for himself. Complete blood count showed left shift with eosinophilia (0.96 x 109/L). Infectious evaluation was negative. His erythroderma and cachexia were concerning for cutaneous T-cell lymphoma (CTCL). A computed tomography scan of the chest, abdomen, and pelvis showed inguinal lymphadenopathy. Skin biopsy showed subacute spongiosis, which could be seen in CTCL or benign dermatitis. Lymph node biopsies showed no lymphoproliferative disorder. Peripheral flow cytometry showed 30% of T-cells with a clonal CD4+CD26- phenotype and peripheral T-cell receptor (TCR) gene rearrangement was positive, suggesting a diagnosis of Sezary syndrome, a systemic form of CTCL.
He was discharged with topical steroids for pruritus and close oncology follow-up. One month later, without any additional intervention, his rash had resolved. This was an unexpected finding for CTCL. Repeat TCR gene rearrangement studies returned negative and only 21% of T-cells had a clonal CD4+CD26- phenotype. The oncologist recognized that T-cell clonality can be seen in benign skin conditions. Accordingly, the diagnosis was revised from Sezary syndrome to severe atopic dermatitis.
Discussion: Atopic dermatitis is a common condition managed by hospitalists, affecting 5-10% of U.S. adults and in severe cases can present with erythroderma. It can mimic many other diagnoses including contact dermatitis, drug reactions, nutritional and immune deficiencies, and CTCL.
The diagnosis of Sezary syndrome requires: (1) an abnormal clonal T-cell population (ex: ≥30% of CD4+ T-cells are CD4+CD26-), (2) peripheral TCR gene rearrangement, and (3) erythema over ≥80% of body surface area. However, T-cell clonality and erythroderma can be seen in benign skin inflammation, particularly in patients over 60 years old. It remains unclear if these benign dermatologic conditions are truly non-malignant or represent early disease that will progress to CTCL. Skin biopsy morphology may not definitively distinguish CTCL from atopic dermatitis, as spongiosis can be seen in either condition. Though not assessed here, matching skin and blood TCR gene rearrangements would support a diagnosis of Sezary syndrome. This patient’s improvement with topical steroids suggested a benign etiology.
Conclusions: Clinicians should be aware that erythrodermic atopic dermatitis can mimic CTCL and initial flow cytometry results may be misleading, particularly when T-cell clonality is near the threshold for CTCL diagnosis. Repeat assessment and additional testing may help confirm the diagnosis. Given the concern for underlying malignancy in cases of erythroderma of uncertain etiology, longitudinal dermatologic follow-up is necessary.