Alzheimer's disease

Vascular dementia

 Multi-infarct

 Diffuse white matter disease (Binswanger's)

Alcoholism^a

PDD/LBD spectrum

Drug/medication intoxication^a

Vitamin deficiencies

 Thiamine (B₁): Wernicke's encephalopathy^a

 B₁₂ (subacute combined degeneration)^a

 Nicotinic acid (pellagra)^a

Endocrine and other organ failure

 Hypothyroidism^a

 Adrenal insufficiency and Cushing's syndrome^a

 Hypo- and hyperparathyroidism^a

 Renal failure^a

 Liver failure^a

 Pulmonary failure^a

Chronic infections

 HIV

 Neurosyphilis^a

 Papovavirus (JC virus) (progressive multifocal leukoencephalopathy)

 Tuberculosis, fungal, and protozoal^a

 Whipple's disease^a

Head trauma and diffuse brain damage

 Chronic traumatic encephalopathy

 Chronic subdural hematoma^a

 Postanoxia

 Postencephalitis

 Normal-pressure hydrocephalus^a

Intracranial hypotension

Neoplastic

 Primary brain tumor^a

 Metastatic brain tumor^a

 Paraneoplastic/autoimmune limbic encephalitis^a

Toxic disorders

 Drug, medication, and narcotic poisoning^a

 Heavy metal intoxication^a

 Organic toxins

Psychiatric

 Depression (pseudodementia)^a

 Schizophrenia^a

 Conversion disorder^a

Degenerative disorders

 Huntington's disease

 Multisystem atrophy

 Hereditary ataxias (some forms)

 Frontotemporal lobar degeneration spectrum

 Multiple sclerosis

 Adult Down's syndrome with Alzheimer's disease

 ALS-parkinsonism-dementia complex of Guam

 Prion (Creutzfeldt-Jakob and Gerstmann-Sträussler-Scheinker diseases)

Miscellaneous

 Sarcoidosis^a

 Vasculitis^a

 CADASIL, etc.

 Acute intermittent porphyria^a

 Recurrent nonconvulsive seizures^a

Additional conditions in children or adolescents

 Pantothenate kinase-associated neurodegeneration

 Subacute sclerosing panencephalitis

 Metabolic disorders (e.g., Wilson's and Leigh's diseases, leukodystrophies, lipid storage diseases, mitochondrial mutations)