Drug-induced cerebral glucose metabolism resembling Alzheimer's Disease: a case study

With aging of society the absolute number and the proportion of patients with cognitive deficits increase. Multiple disorders and diseases can foster cognitive impairment, e.g., Alzheimer's disease (AD), depressive disorder, or polypharmacy.

A 74 year old man presented to the Old Age Psychiatry Service with cognitive deficits while being treated for recurrent depressive episodes and essential tremor with Venlafaxine, Lithium, and Primidone. Neuropsychological testing revealed a medio-temporal pattern of deficits with pronounced impairment of episodic memory, particularly delayed recall. Likewise, cognitive flexibility, semantic fluency, and attention were impaired. Positron emission tomography (PET) with fluorodeoxyglucose was performed and revealed a pattern of glucose utilization deficit resembling AD. On cessation of treatment with Lithium and Primidone, cognitive performance improved, particularly episodic memory performance and cognitive flexibility. Likewise, glucose metabolism normalized. Despite normalization of both, clinical symptoms and glucose utilization, the patient remained worried about possible underlying Alzheimer's disease pathology. To rule this out, an amyloid-PET was performed. No cortical amyloid was observed.

Pharmacological treatment of older subjects may mimic glucose metabolism and clinical symptoms of Alzheimer's disease. In the present case both, imaging and clinical findings, reversed to normal on change of treatment. Amyloid PET is a helpful tool to additionally rule out underlying Alzheimer's disease in situations of clinical doubt even if clinical or other imaging findings are suggestive of Alzheimer's disease.