Differential Diagnosis
- Single most likely diagnosis
- Gastrointestinal Stromal Tumor (GIST) with SIADH: The presence of a large ulcerated GIST in the fundus of the stomach, along with the patient's symptoms and laboratory findings consistent with SIADH, makes this the most likely diagnosis. The spindle cell variant is a common subtype of GIST.
- Other Likely diagnoses
- Other gastric malignancies (e.g., gastric adenocarcinoma): Although the biopsy showed a spindle cell variant, other gastric malignancies could also cause SIADH and similar symptoms.
- Metastatic disease to the stomach: Metastases to the stomach from other primary sites (e.g., breast, lung, or melanoma) could also lead to SIADH and similar clinical presentation.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Gastric lymphoma: Although less common, gastric lymphoma can cause SIADH and similar symptoms, and missing this diagnosis could have significant consequences.
- Gastric carcinoid tumor: Carcinoid tumors can produce various hormones, including ADH, leading to SIADH, and can be aggressive if not diagnosed and treated promptly.
- Rare diagnoses
- Ectopic ADH-producing tumor (e.g., small cell lung cancer): Although rare, ectopic ADH production from a tumor outside the stomach could cause SIADH, and the presence of a GIST could be coincidental.
- Inflammatory or infectious causes of SIADH (e.g., tuberculosis, sarcoidosis): These conditions can cause SIADH, but would be less likely given the presence of a GIST and the patient's clinical presentation.