Young-onset Alzheimer’s dementia mimicking progressive myoclonic epilepsy spectrum

Abstract Background Young-onset Alzheimer’s dementia (YOAD) refers to the onset of disease before the age of 40 years. Classical AD typically presents with memory impairment with involvement of other cognitive domains like language, visuospatial orientation. On contrary, YOAD shows phenotypic heterogeneity in the form of predominant psychiatric disturbances apart from dementia and rarely seizures, cerebellar ataxia. We report a 36-year-old lady with dementia, myoclonus, seizures and cerebellar ataxia of 3 year duration mimicking progressive myoclonic epilepsy (PME) spectrum who had novel missense mutation in PSEN1 gene (L226F) suggestive of YOAD. Case presentation A 36-year-old lady presented with seizures in the form of generalized tonic–clonic seizures of 3 year duration followed by multifocal myoclonic jerks, cognitive decline of 2 year duration and imbalance while walking of 1 year duration. Montreal cognitive assessment (MOCA) score was 6/30. Addenbrooke’s cognitive examination III (ACE-III) score was 16/100. The mental status examination showed diffuse impairment of lobar functions. Brain magnetic resonance imaging showed diffuse cerebral and cerebellar atrophy. Skin biopsy did not show Lafora bodies or dermal inclusions on electron microscopy. Whole exome sequencing showed pathogenic missense variant NM_000021.4(PSEN1):c.676C > T (p.Leu226Phe) in PSEN1 gene suggestive of YOAD. Conclusions YOAD due to PSEN1 mutation has to be considered in patients with cerebellar ataxia, seizures, myoclonus, dementia with psychiatric disturbances. This case highlights the high index of suspicion for differential diagnosis of YOAD in patients with young-onset dementia with ataxia, seizures and myoclonus.