[A case of behavioral variant frontotemporal dementia presenting with frequent laughter during conversations].

We describe a case of behavioral variant frontotemporal dementia (bvFTD) presenting with frequent laughter during conversations. A 72-year-old male patient visited our hospital because of aspontaneity and abnormal behaviors. His medical history revealed epilepsy attacks approximately five years prior, which improved following administration of antiepileptic drugs. At the age of 67 years, the patient began exhibiting aspontaneity and abnormal behaviors, such as leaving a teahouse without paying for his coffee. Neurological examinations indicated moderate dementia and bradykinesia while walking. The patient frequently laughed during conversations with his wife and doctor, creating the impression that he was euphoric. His laughter was neither explosive nor obsessive, and did not involve loss of consciousness or seizures. MRI of the head revealed symmetrical atrophy of the bilateral frontal lobes. SPECT demonstrated decreased cerebral blood flow in the bilateral frontal lobes, particularly in the outer and inner frontal convexities. Based on the patient's clinical history and imaging results, a diagnosis of bvFTD was established. Our literature review identified only one research paper discussing the frequency of laughter in frontotemporal dementia, which suggested that patients with bvFTD laugh less often. However, several reports indicated that patients with FTD exhibit euphoric behaviors more frequently compared to those with other forms of dementia. We hypothesize that euphoric patients with bvFTD may laugh more frequently during conversations, reflecting disorders of emotional expression and a loss of empathy.