In this article, we review and repropose our hypothesis of the endogenous appearance of anticholinergic activity (AA) in Alzheimer's disease (AD). First, we introduce our previous articles and speculate that, because acetylcholine (ACh) regulates both cognitive function and inflammation, downregulation of this neurotransmitter causes upregulation of the inflammatory system. AA then appears endogenously with the production of cytokines and the downregulation of ACh in AD. To support our hypothesis, we present a female AD patient whose AA was considered to occur endogenously through her AD pathology. Her serum anticholinergic activity (SAA) was positive at her first visit to our memory clinic, was negative at the 1-year and 2-year follow-up visits, and had become positive again by 3 years. We speculate that the initial positive SAA was related to her AD pathology plus mental stress, and that her SAA at 3 years was related to her AD pathology only. Consequently, we believe that 2 patterns of SAA positivity (and therefore AA) exist. One occurs when the downregulation of ACh reaches a critical level, and the other occurs with the addition of some other factor such as medication, induced illness or mental stress that causes AA to affect AD pathology. Finally, we consider the pharmacotherapy of AD based on the proposed hypothesis and conclude that cholinesterase inhibitors can be used to prevent rapid disease progression, whereas N-methyl-D-aspartate receptor antagonists should be reserved for the treatment of AD that is already in a stage of rapid progression. We also propose a staging schema for patients with AD.

We previously proposed the hypothesis of endogenous anticholinergic activity (AA) in Alzheimer's disease (AD). According to this hypothesis, the downregulation of acetylcholine seen in AD is associated with upregulation/hyperactivity of N-methyl-D-aspartate receptor (NMDAR). The hyperactivation of NMDAR then induces inflammation, which, in turn, causes AA to appear endogenously. Based on this hypothesis, we commented that cholinesterase inhibitors (ChEIs) are ‘preventative' therapy for AD and NMDAR antagonists are the true ‘treatment' for AD. We also noted that ChEIs, such as donepezil, could treat delirium. Moreover, we proposed measuring serum anticholinergic activity in patients, particularly AD patients, in out-of-hospital pharmacies to monitor the anticholinergic burden for targeted treatment.

We report a case of a 54-year-old woman presenting with amnesia, apathy, work-related difficulties and mental stress. At presentation, her Mini-Mental State Examination score was 27 and her serum anticholinergic activity (SAA) was positive without medication or recent physical illnesses. In addition, magnetic resonance imaging revealed mild atrophy of the frontal and temporal lobes, with a relatively intact hippocampus. Consequently, we diagnosed mild cognitive impairment due to Alzheimer's disease and prescribed a cholinesterase inhibitor (donepezil, 10 mg/day); her SAA fully disappeared and clinical symptoms partially resolved. Addition of duloxetine coupled with environmental adjustments caused her cognitive function to return to a normal level, so we diagnosed pseudodementia due to depression. In this case, we believe that the simultaneous cholinergic burden and mental stress led to positive SAA, which made it reasonable to prescribe a cholinesterase inhibitor to ameliorate the associated acetylcholine hypoactivity. We believe that it is essential to recognize the importance of prescribing a cholinesterase inhibitor for specific patients, even those with pseudodementia, to control their clinical symptoms. Moreover, SAA might be a useful biomarker for identifying this subgroup of patients. We propose that anticholinergic activity appears endogenously in mood disorders (depression and bipolar disorder) and set out our rationalization for this hypothesis.