[Cutaneous plasmacytosis with Darier's sign in a woman of European origin]. / Plasmocytose cutanée avec signe de Darier chez une femme d'ascendance européenne.

INTRODUCTION: Cutaneous plasmacytosis is a rare skin condition first described in 1976 and it is seen mainly in patients of Asian descent. Patients usually present with multiple reddish-brown macules and nodules chiefly on the trunk and face, with clusters of well-differentiated plasma cells in the dermis. The aetiopathogenesis and nosological features of this entity remain obscure. We report herein a case of cutaneous plasmacytosis in a European middle-aged woman with presence of Darier's sign. PATIENTS AND METHODS: A 56-year-old woman of European descent presented with asymptomatic hyperpigmented patches affecting the dorsal aspect of her trunk for at least two years. Darier's sign was present in some episodes. Cutaneous biopsy showed a moderately dense interstitial and perivascular infiltrate containing numerous well-differentiated mature plasma cells affecting the entire dermal surface. Kappa and lambda immunochemistry demonstrated polyclonal plasma cell infiltrates with absence of light-chain restriction. Immunohistochemical examination was negative for HHV-8 and Treponema pallidum spirochetes. Laboratory findings revealed hypergammaglobulinaemia with no monoclonal bands being detected on immunofixation. A diagnosis of cutaneous plasmacytosis was made. In the absence of systemic involvement initial management consisted of clinical surveillance. DISCUSSION: The characteristic clinico-pathological features of CP allowed diagnosis of this skin condition in our patient, although it is very rarely reported in patients of European descent. The main differential diagnoses were ruled out, namely plasmacytic infiltrates related to infections and marginal B-cell lymphoma.

Neutrophilic dermatoses.

Neutrophilic dermatoses (ND) are a group of inflammatory skin conditions characterized by a neutrophilic infiltrate on histopathology with no evidence of infection. ND are classified based upon the localization of neutrophils within the skin and clinical features. Recent findings suggest that ND are due to two main mechanisms: i) a polyclonal hereditary activation of the innate immune system (polygenic or monogenic); or ii) a clonal somatic activation of myeloid cells such as encountered in myelodysplastic syndrome or VEXAS syndrome. ND belong to internal medicine as a great number of patients with ND suffer from an underlying condition (such as hematological malignancy, inflammatory bowel disease, auto-immune and auto-inflammatory diseases). ND are diagnoses of exclusion and physicians should always consider differential diagnoses, particularly skin infections. Here, we review the pathophysiology and classification of the main ND (i.e., subcorneal pustular dermatosis (Sneddon-Wilkinson Disease) and Intercellular IgA dermatoses, aseptic pustulosis of the folds, Sweet syndrome, neutrophilic eccrine hidradenitis, pyoderma gangrenosum, erythema elevatum diutinum, neutrophilic urticarial dermatosis and neutrophilic panniculitis), their clinical and histopathological features, and we highlight the investigations that are useful to identify ND-associated diseases and to exclude the differential diagnoses.