Unmasking systemic mastocytosis: a case of gastrointestinal involvement misdiagnosed as achalasia.

Systemic mastocytosis (SM) is a rare myeloproliferative neoplasm characterized by the clonal proliferation of mast cells in various organs, including the gastrointestinal (GI) tract. GI manifestations of SM, often non-specific, can lead to misdiagnosis, with symptoms overlapping those of common disorders such as achalasia, eosinophilic gastroenteritis, and inflammatory bowel disease. This case report details the diagnosis and management of an 83-year-old female with progressive dysphagia and weight loss, initially suspected to have achalasia. Following further investigation, SM was diagnosed based on histopathologic findings, including mast cell infiltration and CD117 and tryptase positivity, as well as molecular confirmation of the KIT D816V mutation. The case emphasizes the importance of a multidisciplinary diagnostic approach combining endoscopy, histopathology, and molecular testing to distinguish SM from other GI disorders. Early recognition, along with tailored treatment strategies, is essential for improving patient outcomes in SM with GI involvement.