A Case of Early-Onset Alzheimer’s Disease With Comorbid Schizophrenia: Diagnostic and Therapeutic Challenges

Early-onset Alzheimer's disease (EOAD) is defined as symptom onset before the age of 65.The disease frequently presents with prominent psychiatric features such as psychosis, behavioral disturbances, and personality changes, which can overlap with schizophrenia, creating a significant diagnostic challenge.The coexistence of EOAD and schizophrenia is rare, which can cause a delay in the recognition of the underlying neurocognitive disorder.We present a 58-year-old female patient with EOAD and comorbid schizophrenia who had progressive cognitive decline, behavioral disturbances, hallucinations, and functional and memory impairment.Neuroimaging demonstrated significant cerebral atrophy, supporting the diagnosis of a neurodegenerative process in conjunction with the patient's clinical presentation.The patient is managed on maintenance therapy with paliperidone palmitate 156 mg monthly injection, donepezil 10 mg at night, benztropine 2 mg at night, and memantine 10 mg twice daily.Following the long-acting injectable antipsychotic therapy, medication adherence improved, and psychiatric symptoms remained relatively stable despite ongoing cognitive decline.The patient was seen at an outpatient clinic for four years, and longitudinal outpatient follow-up over this period required minor adjustments to the treatment regimen.This case highlights the diagnostic complexity of EOAD presenting alongside schizophrenia, where the psychiatric manifestations may obscure the recognition of the underlying neurodegenerative disorder.It highlights the importance of maintaining EOAD in the differential diagnosis of patients with progressive cognitive decline, behavioral changes, and psychotic symptoms, particularly when functional impairment worsens over time.Furthermore, this case demonstrates the potential role of long-acting injectable antipsychotics combined with cognitive-enhancing therapies in promoting treatment adherence and maintaining psychiatric stability.This case contributes to the limited literature on EOAD coexisting with schizophrenia and the multidisciplinary longitudinal management and approach to optimize patient outcomes and preserve quality of life in complex neuropsychiatric conditions.