Mastocytosis is characterized by mast cell infiltration in various tissues and organs. More than half of the patients are children. Pediatric mastocytosis has several features that differentiate the disease from adult mastocytosis. Importantly, the disease, which usually starts in the first months of life or at birth, often shows a transient course with spontaneous resolution in adolescence. In most children, mastocytosis is limited to skin. Cutaneous involvement can present as maculopapular cutaneous mastocytosis, mostly with the polymorphic variant, cutaneous mastocytoma, or diffuse cutaneous mastocytosis. When children present with monomorphic maculopapular skin lesions, the variant typically seen in adults, this may indicate rare persistent disease until adulthood, often associated with systemic mastocytosis. Many pediatric patients suffer from symptoms of mast cell activation, ranging from pruritus to flushing and blistering. Children with cutaneous mastocytosis typically exhibit mutations in various regions of the KIT gene, whereas those with systemic disease predominantly carry KIT D816V. Diagnosis is mainly based on noninvasive measures, including skin inspection, elicitation of the Darier's sign, and analyses of the serum tryptase and KIT variant in blood. Treatment options encompass avoidance of triggers of mast cell activation, H1 and H2 antihistamines, cromolyn, and omalizumab. In children with systemic mastocytosis, tyrosine kinase inhibitors tailored to the specific KIT variant may be considered.

Mastocytosis is characterized by the clonal infiltration and proliferation of neoplastic mast cells into target organs. Clinical features of mastocytosis are based in large part on dysregulated mast cell mediator release. Affected individuals may present with isolated skin involvement or multisystemic disease with a spectrum of symptoms including anaphylaxis, pathologic fractures, and chronic gastrointestinal, neurocognitive, musculoskeletal, and constitutional symptoms. The term "mastocytosis in the skin" refers to individuals with cutaneous infiltration and encompasses both localized and systemic forms of disease. Cutaneous involvement is further categorized into cutaneous mastocytoma, diffuse cutaneous mastocytosis, and maculopapular cutaneous mastocytosis based on morphology. In ~95% of patients with systemic mastocytosis, the disease is driven by the KIT D816V somatic variant. The aim of this clinical review is to highlight the diagnostic considerations, management complexities, and evolving treatment landscape that must be considered when evaluating a patient presenting with mastocytosis in their skin. Clinical manifestations, histopathology, and laboratory parameters are essential to diagnosis and determining the disease burden in those with known or suspected systemic mastocytosis. Once appropriately staged, both skin-directed therapy as well as novel systemic treatment options, including selective tyrosine kinase inhibitors, can be considered with the potential to improve patient outcomes.

Mastocytosis is characterized by the proliferation of neoplastic mast cells in various organs, which can have either cutaneous or systemic presentation. Solitary cutaneous mastocytomas are most commonly seen in the pediatric age group but rarely present in adults. Histopathology of cutaneous mastocytoma is well described in the literature but only a few studies are available describing the cytomorphological features. We present a case of a 19-year-old female who presented with a 6-month history of a right supraclavicular single, 0.5 × 0.5 cm, well-defined, reddish-brown round nodule. The fine needle aspiration cytology (FNAC) smears were highly cellular showing monomorphic cells, predominantly dispersed singly and occasionally in small clusters. The cells were round to oval, with moderate cytoplasm containing coarse metachromatic granules. Toluidine blue stain and CD117 immunocytochemical stain confirmed the presence of mast cell granules. Based on the cytomorphology, staining, clinical history, and examination, a diagnosis of solitary cutaneous mastocytoma was rendered. FNAC plays a pivotal role in diagnosing mast cell tumors and even obviates the need for tissue biopsy in selected cases.