Prior to a diagnosis of dementia due to Alzheimer disease, many patients experience mild cognitive impairment (MCI) as a prodromal syndrome. The amnestic type of MCI is a risk factor for subsequent progression to Alzheimer disease. Patients with MCI have a 15% chance every year of progressing to meet criteria for dementia.
Alzheimer disease is the most common type of dementia, accounting for 50%-75% of dementia diagnoses. The incidence increases with age, with about a 1% incidence at age 65 and an 8% incidence for patients aged 85 and over. Most cases occur sporadically; however, a small percentage of cases are familial. Less than 10% of Alzheimer disease patients are diagnosed prior to age 65 and are considered to have an early-onset form of the disease; these patients are the most likely to have a familial form of the disease.
A diagnosis of possible or probable Alzheimer disease can be made clinically based on history and examination. Neuropsychological testing or other forms of cognitive testing may aid in making the diagnosis. When Alzheimer disease is suspected, it is recommended to check several laboratory studies to rule out other potentially treatable causes of dementia. Neuroimaging may support the diagnosis of Alzheimer disease, particularly if it reveals temporal lobe and hippocampal atrophy. Several biomarkers including cerebrospinal fluid (CSF) studies and PET imaging are also under investigation as possible diagnostic tools. However, postmortem pathological examination is required to confirm a suspected diagnosis of Alzheimer disease.
Patients with this disorder may have an increased risk of various general medical conditions.
G30.9 – Alzheimer's disease, unspecified
26929004 – Alzheimer's disease
Differential Diagnosis & Pitfalls
- Frontotemporal dementia
- Vascular dementia
- Lewy body dementia
- Progressive supranuclear palsy
- Corticobasal syndrome
- Parkinson disease dementia (see dementia)
- Normal pressure hydrocephalus
- Mild cognitive impairment
- Vitamin B12 deficiency
- Chronic traumatic encephalopathy
- Creutzfeldt-Jakob disease
- Subclinical status epilepticus
- Human immunodeficiency virus (HIV) / AIDS dementia
- Huntington disease
- Wilson disease
- Chronic alcohol or drug abuse (eg, Wernicke-Korsakoff syndrome)
- Infectious encephalitis (eg, herpes simplex virus encephalitis)
- Paraneoplastic encephalitis