Case Report: Bilateral tonic-clonic seizures as initial presentation of Lhermitte–Duclos Disease and Cowden Syndrome

Lhermitte–Duclos Disease is a rare, benign cerebellar tumour that is a manifestation of Cowden Syndrome, a hereditary tumour predisposition syndrome caused by germline mutations in the PTEN gene. Here, we report a 38-year-old female patient with no past medical history or family neurological history presenting to hospital with a new, unprovoked, bilateral tonic-clonic seizure with no apparent seizure focus. EEG showed no epileptiform activity, and 7T MRI demonstrated bilateral Lhermitte–Duclos Disease as well as several cortical meningoencephaloceles. Her seizures were controlled with levetiracetam, and given her cerebellar lesion was minimally symptomatic, no further interventions were pursued. PTEN germline testing identified a heterozygous c.1003C>T (p.Arg335*) variant known to be pathogenic for Cowden Syndrome, and we promptly referred this patient for cancer screening. She was diagnosed with ductal carcinoma in situ and thyroid atypia of undetermined significance, and she subsequently underwent bilateral mastectomy and total thyroidectomy respectively. Lhermitte–Duclos Disease and Cowden Syndrome may present initially in previously healthy patients with bilateral tonic-clonic seizures without clear epileptogenic foci. Recognition of the underlying hereditary cancer syndrome enables timely cancer detection, potentially improving treatment outcomes.