Frail, Fluid, and Falsely Accused: Myxedema Ascites in an Older Adult.

Ascites is a rare presentation of hypothyroidism and can be easily mistaken for malignancy when it occurs alongside pleural effusion and radiological lymphadenopathy. We report the case of a 63-year-old man who presented with progressive generalized anasarca, abdominal distension, and worsening breathlessness. Diagnostic paracentesis revealed exudative ascites with a low serum-ascites albumin gradient (SAAG) and markedly elevated protein content, and thyroid function testing showed profound, previously undiagnosed primary hypothyroidism (thyroid-stimulating hormone (TSH) 221.2 µIU/mL). On a subsequent admission, contrast-enhanced CT additionally revealed bilateral pleural effusion with mediastinal lymphadenopathy and omental fat stranding, raising concern for an underlying malignant or granulomatous process. Repeat ascitic fluid analysis, cytology, tumor markers, and cartridge-based nucleic acid amplification test (CBNAAT) were unremarkable, and an omental biopsy was performed and was not suggestive of inflammatory pathology; in view of this reassuring result, together with the patient's frailty and early clinical improvement, the higher-risk procedure, mediastinal lymph node biopsy, was deferred by multidisciplinary consensus in favor of a trial of thyroid hormone replacement. This strategy proved correct: with initiation and titration of levothyroxine, the patient's ascites, pleural effusion, and edema resolved completely on serial follow-up, obviating the need for mediastinal lymph node sampling. This case illustrates that myxedema ascites can radiologically mimic malignancy and that thyroid function testing, together with judicious, risk-stratified tissue sampling and, where clinically appropriate, a closely monitored trial of thyroid hormone replacement, can help a frail older adult avoid an unnecessary high-risk biopsy.