A 58-year-old man with a history of smoking was admitted with a 3-month history of an unsteady gait, vertigo, two falls, a 15-pound weight loss, and hematemesis. He underwent an emergent upper endoscopy, which revealed a discrete 3-cm ulcerated mass in the third portion of the duodenum. Computed tomography (CT) of the head demonstrated multiple hyperdense lesions throughout the cerebellum and cerebrum. A CT of the abdomen/pelvis demonstrated an area of small bowel-to-small bowel intussusception at the site of the duodenal mass and multiple hyperdensities in bilateral lungs, left adrenal gland, and enlarged gastrohepatic and retroperitoneal lymph nodes. Duodenal mass biopsy showed melanoma; a full skin exam revealed no lesions consistent with melanoma. He was diagnosed with metastatic melanoma of unknown primary. He was treated with whole brain radiation and palliative chemotherapy; he died within six months of diagnosis.
Only 2% of all metastatic melanomas are without a known primary site. This type of presentation is speculated to be from a spontaneously regressed primary melanoma, a misdiagnosed skin lesion, or a de novo malignant transformation. The GI tract is a well-known metastatic site for melanomas, and the small bowel is the second most common site for metastases. Approximately 50-60% of metastatic lesions are noted in the liver, 35-50% appear in the small bowel, 15-30% happen in the colon, and 5-20% are found in the stomach. These lesions tend to be clinically insignificant, often found inadvertently in the workup of previously diagnosed melanoma. One autopsy series of patients who died from metastatic melanoma noted that the GI tract was affected in 60% of all patients, although only 1-4% were clinically diagnosed ante mortem. Only one case report noted a gastrointestinal tract bleed as the initial presentation of a gastric melanoma lesion. Patients with visceral metastases have a dismal prognosis, generally dying within six months of diagnosis.
Although uncommon as the initial presentation, metastatic lesions from melanoma should be considered as a potential etiology for GI bleeds. A prior diagnosis of melanoma is not required to place it on the differential, as demonstrated in this case of metastatic melanoma of unknown primary. Overall prognosis is very poor for patients with visceral metastatic lesions at time of diagnosis.