Epilepsy is frequently accompanied by psychiatric symptoms, including mood disturbances such as depression, irritability and euphoria. Interictal dysphoric disorder (IDD), characterised by depressive and affective symptoms, is typically managed with psychiatric treatment. However, persistent symptoms, despite adequate psychiatric intervention, may indicate an underlying epileptogenic mechanism.

To highlight the importance of recognising epileptogenic contributions to persistent psychiatric symptoms, even in patients with apparently well-controlled epilepsy.

We present a case report of a Japanese woman in her 40s with well-controlled epilepsy; however, she developed enduring psychiatric symptoms. Clinical features, psychiatric treatments, neurological evaluation and therapeutic outcomes are described.

The patient experienced anxiety, depression, irritability and fear, leading to an initial diagnosis of IDD. Treatment with escitalopram and olanzapine achieved only partial symptom relief. Residual symptoms prompted further investigation, which revealed symptoms suggestive of temporal lobe epilepsy auras. Adjustment of anti-seizure therapy with lacosamide resulted in complete resolution of psychiatric symptoms, marked functional recovery and a reduction in her Hamilton Depression Rating Scale (HAMD-17) score improved from 23 to 6.

This case highlights that even in apparently well-controlled epilepsy persistent psychiatric symptoms may indicate an underlying epileptogenic mechanism rather than a primary psychiatric disorder. Careful evaluation and appropriate optimisation of anti-seizure medication can yield substantial psychiatric and functional improvements, underscoring the importance of multidisciplinary assessment in such presentations.