Every dementia has a prodrome. The clinical question is how long, how recognizable, and how modifiable. Alzheimer’s pathology — amyloid accumulation, then tau, then neurodegeneration — begins fifteen to twenty years before clinical symptoms become apparent. The actual cognitive inflection, the bending of the curve that an attentive clinician can recognize, typically becomes detectable five to ten years before formal diagnostic criteria for dementia are met. The window between the inflection and the diagnosis is the window in which longevity psychiatry has its highest clinical leverage.
The earliest signals are subtle, and they are often dismissed. They include: subtle changes in word retrieval beyond what the patient considers normal aging; increasing reliance on written reminders to a degree the patient or their family notices; difficulty learning new technologies that the patient used to be able to acquire; spousal reports of repetition — "he tells me the same story twice in an afternoon"; missed appointments that the patient has historically and reliably kept; and, importantly, patient self-report that "something is different." None of these alone confirms pathology. The cluster, in a patient who used to function differently, is the signal.
Patient self-report deserves more weight than it is often given. Subjective Cognitive Decline (SCD), where a patient feels something is wrong before any objective test can detect it, is associated with elevated risk of later MCI and dementia. Studies have followed SCD cohorts for years and found that the patients who reported feeling subjectively different were correctly identifying their own trajectory ahead of any test. The dismissive clinical response — "you're fine, everyone forgets things" — is sometimes correct and sometimes a missed inflection. The clinical discipline is to take SCD seriously while distinguishing it from worry-driven false alarm.
The objective signals come from formal cognitive testing. The Montreal Cognitive Assessment (MoCA) detects mild cognitive impairment more sensitively than the Mini-Mental State Exam (MMSE), which is too easy at the high end. A drop in MoCA from a prior baseline matters more than a single absolute score — which is why baseline measurement in asymptomatic patients matters so much. Executive function testing — clock drawing, Trail Making B, verbal fluency — catches early frontotemporal and vascular contributions that pure memory testing misses. Formal neuropsychological testing, when available, gives the most diagnostic clarity in ambiguous cases.
The differential at the inflection is wide, and the work of differentiating is the actual clinical task. Apparent early cognitive decline can be: medication side effects (anticholinergics, sedatives, polypharmacy in older adults); depression (so-called pseudodementia, where treated depression restores cognition to baseline); sleep apnea (intermittent hypoxia and sleep fragmentation produce cognitive presentations that resolve with treatment); hypothyroidism; B12 and folate deficiency; alcohol use; normal pressure hydrocephalus; chronic pain medications; and treatable sleep disorders beyond apnea. Every reversible contributor must be considered, because every reversible contributor that is found and treated buys real time.
The non-reversible contributors must also be considered, because clarity of diagnosis informs both treatment and family planning. Alzheimer’s disease, vascular cognitive impairment, frontotemporal degeneration, Lewy body disease, and mixed pathology each have different trajectories, different treatment implications, and different family conversations. The first task is to identify and treat the reversible. The second is to clarify the irreversible. Both tasks are part of the longevity-psychiatry workup at the inflection.
Recognizing the inflection is the single highest-leverage clinical skill in this volume. The patient identified at MCI has a meaningfully different trajectory than the patient identified three years later at clear dementia. Anti-amyloid therapy is approved for MCI and early AD but not for established moderate dementia. Lifestyle and risk-factor modification has its largest effect when applied during the inflection rather than after. The intervention window is real, and once it closes, what remains is treatment of established disease rather than redirection of trajectory.