Periorbital hyperpigmentation as the initial manifestation of smoldering multiple myeloma in a patient with coexisting gastrointestinal stromal tumor: a case report and narrative literature review.

Periorbital hyperpigmentation (POH) as the sole initial manifestation remains undescribed in patients with smoldering multiple myeloma (SMM) without amyloid deposition, and the coexistence of SMM with gastrointestinal stromal tumor (GIST) is exceptionally rare. We describe a 56-year-old male who was treated with imatinib for eight months after resection of a low-risk gastric GIST and developed bilateral symmetric POH. Workup revealed IgA κ-type monoclonal gammopathy and 3% abnormal plasma cells on bone marrow aspiration. Further biopsies of bone marrow and abdominal wall fat excluded amyloid deposition. Therefore, a diagnosis of SMM (IgA κ-type) was made. To the best of our knowledge, this is the first reported case of SMM presenting with isolated POH in the absence of light-chain (AL) amyloidosis and coexisting with a GIST. This case suggests that POH may represent a rare early cutaneous manifestation of SMM and may further broaden the recognized clinical spectrum of SMM.