CONCLUSIONS Myxedema coma is an important differential diagnosis in critically ill patients. Early diagnosis and treatment are paramount but challenging due to a lack of diagnostic criteria. We report a case about a patient who suffered from untreated hypothyroidism for several years. Before the correct diagnosis was made, he was admitted three times due to severe constipation. Eventually, he developed myxedema coma in connection with a urinary tract infection. The course was complicated by recurrent seizures, and neuroimaging showed bilateral hygromas. Hormone replacement therapy resulted in complete recovery and regression of hygromas. To the best of our knowledge, this is the first time hygroma is reported in association with myxedema coma. CONCLUSIONS Myxedema coma is a difficult diagnosis to make due to a lack of diagnostic criteria. Cardinal features include hypothermia, bradycardia, gastrointestinal symptoms, pericardial/pleural effusions and affection of CNS. Anemia and hyponatremia are common. In case of suspected myxedema coma, neuroimaging should be a part of the evaluation in most cases. There is a possible association between longstanding/severe hypothyroidism and hygroma.