Histologic Pitfall in Sweet Syndrome

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Summary and Comment

Histologic Pitfall in Sweet Syndrome

A new finding challenges the traditional histologic criteria for Sweet syndrome.

Sweet syndrome (SS) is a neutrophilic dermatosis characterized by erythematous, painful nodules or plaques in patients with fever, leukocytosis, and neutrophilia. The syndrome has three subtypes: (1) SS that is idiopathic or associated with inflammatory disorders (80%–90% of cases), (2) SS associated with hematologic malignancies, and (3) SS associated with solid, malignant visceral neoplasms. Our understanding of the characteristic histologic features has changed over time; for example, we now recognize a secondary vasculitis in some cases. These authors reviewed data on 41 patients with fresh, clinically typical lesions of SS (two thirds were women; median age, 53) and report a new histologic association: an inflammatory infiltrate of histiocytoid mononuclear cells or immature myeloid cells instead of mature neutrophils.

Biopsy samples showed an inflammatory infiltrate of histiocyte-like cells in fresh, clinically typical SS lesions in these patients. Histologic evaluation showed mild, unspecific epidermal changes (e.g., spongiosis and exocytosis of inflammatory cells); moderate-to-intense papillary dermal edema; and a band-like infiltrate of the superficial and mid-dermal mononuclear cells, which had large, slightly eccentric, twisted or kidney-shaped basophilic nuclei with single, inconspicuous nucleoli and slight eosinophilic cytoplasm. Admixed neutrophils were outnumbered by these mononuclear cells. No vasculitis was noted. Most of the mononuclear cells showed immunoreactivity for CD15, CD43, CD45, CD68, MAC-386, HAM56, and lysozyme, indicating a monocytic-histiocytic lineage. Myeloperoxidase and CD66abce were positive in these histiocytic-like cells, suggesting the possibility of myelogenous leukemia. However, peripheral blood showed no significant abnormality (the most common laboratory abnormalities were neutrophilia and elevated levels of ESR and C-reactive protein), and fluorescent in situ hybridization (FISH) tests performed in some patients to identify a bcr/abl gene fusion (present in lesions of myelogenous leukemia cutis) revealed no such fusion. Oral corticosteroid and nonsteroidal anti-inflammatory drugs produced resolution of the lesions, and no leukemia developed over a mean follow-up of 8.2 years.

Comment: Awareness of this histologic presentation will help prevent confusion of these primitive hematopoietic cells with neoplastic proliferations, especially in Sweet syndrome associated with hematologic malignancies. Performance of immunohistochemical and genetic studies to define the nature of the dermal infiltrate and careful follow-up are essential in interpreting these cutaneous lesions and avoiding unnecessary aggressive therapy. The authors of an accompanying editorial present a thought-provoking discussion of the rethinking of Sweet syndrome.

— Angelica Selim, MD

Published in Journal Watch Dermatology September 13, 2005