Hypothyroidism can cause numerous psychiatric symptoms. Fifteen percent of patients with hypothyroidism who present with psychiatric symptoms develop psychotic symptoms, a condition termed"myxedema psychosis". However, only a few cases have been reported in Japan, suggesting that myxedema psychosis is not sufficiently recognized by Japanese physicians. To facilitate the importance of recognizing hypothyroidism as a cause of psychotic symptoms, we report a case of myxedema psychosis with an updated review of the literature.
 A woman in her 50 s was admitted to our hospital with psychotic symptoms. She was diagnosed with Hashimoto's disease 2 years prior and had received levothyroxine. One month before hospitalization, she discontinued levothyroxine treatment on her own. Subsequently, irritability and auditory hallucinations gradually appeared, and she began to wander outside her home. She visited a general hospital with chief complaints of palpitation and anxiety, and was admitted to the internal medicine department with marked hypothyroidism. After admission, risperidone and levothyroxine were prescribed, but the auditory hallucinations and thought disorder persisted. As she also refused to be examined, she was transferred to the psychiatric department of our hospital for further examination and treatment on day 7. Upon admission to our psychiatric department, her auditory hallucinations improved, but her thought disorder, agitation, and hypothyroidism remained. The combination of a mixture of slow waves detected by electroencephalography (EEG) and mild increase in cerebrospinal fluid (CSF) protein levels suggested Hashimoto's encephalopathy. However, as her symptoms improved gradually, the levothyroxine dosage was increased initially and steroids were not administered. The agitation and thought disorder disappeared by the 7th day after transfer, and she was discharged on the 16th day. After discharge, risperidone was gradually discontinued and there was no relapse of psychotic symptoms. Fourteen months after discharge, her psychotic symptoms recurred with increased TSH. After increasing the levothyroxine dosage, the symptoms rapidly improved.
 Based on previous case reports and systematic reviews, myxedema psychosis is a condition with a good prognosis; antipsychotics can be discontinued in favor of thyroid hormone replacement. Thus, when diagnosing and treating patients with psychosis, organic psychosis induced by hypothyroidism should be differentiated from psychoses with other causes.
 Authors' abstract