Dementias Secondary to Other Disorders

Dementia may be secondary to substances (alcohol, drugs, or toxins), infections, prions, structural brain disorders (including normal-pressure hydrocephalus) or to other potentially reversible disorders.

Dementia due to drugs, alcohol, or toxins

Acute ingestion of psychoactive drugs may cause acute mental status changes. Rarely, long-term ingestion of these drugs leads to permanent, irreversible cognitive impairment. The most common form, alcohol-associated dementia, is due to heavy ingestion of alcohol for > 10 yr. Ingestion of other toxic substances (eg, heavy metals) may also cause dementia.

Dementia due to infection

Acute CNS infections may cause delirium; chronic infections may cause dementia, delirium, or both. The most common, HIV-associated dementia, tends to affect a younger population than most other dementias. Although HIV can directly infect and destroy neurons, dementia usually occurs in later stages of the disorder and is rarely a presenting symptom of HIV. Risk is inversely related to the CD4 count. HIV infection also predisposes to brain infection with the JC virus, resulting in progressive multifocal leukoencephalopathy. Other viruses that infect the brain (whether HIV infection is present or not) may cause acute cognitive dysfunction due to encephalitis or chronic cognitive dysfunction due to a postencephalitis syndrome.

Neurosyphilis and Lyme disease, which are spirochetal infections, can cause dementia. These disorders are treatable and at least partially reversible, but a better approach is early recognition plus treatment of the primary infection before the CNS is affected. Rarely, cryptococcal meningitis, a fungal infection, causes dementia.

Dementias caused by prions (Creutzfeldt-Jakob disease and variant Creutzfeldt-Jakob disease) are sometimes classified as infectious. Myoclonus and rapid deterioration are characteristic. Diagnosis is important because these disorders can be transmitted via infected tissue. They have no specific treatment and are fatal.

Dementia due to structural brain disorders

Chronic subdural hematomas: Rarely, chronic subdural hematomas cause dementia. Risk factors for these hematomas include alcoholism, thrombocytopenia, and coagulopathy (including anticoagulant use). Common symptoms are excessive drowsiness, headache, ataxia, and focal neurologic deficits.

Hematomas may not be suspected as a cause of dementia because many patients do not have a clear history of head trauma or risk factors. Diagnosis is by noncontrast CT or, if findings are equivocal, by MRI or contrast CT.

Indications for surgical evacuation include a midline shift detected by neuroimaging and any symptoms other than mild headache. Depending on the duration of the hematoma, evacuation may only partially improve cognitive function.

Normal-pressure hydrocephalus: Normal-pressure hydrocephalus is a syndrome of gait disturbance, urinary incontinence, and dementia in patients with enlarged brain ventricles and normal or slightly elevated CSF pressure. This disorder causes up to 6% of dementia cases.

Normal-pressure hydrocephalus is thought to result from a defect in CSF resorption in arachnoid granulations. Most commonly, the gait disturbance is nonspecific unsteadiness and impaired balance, although a magnetic gait, in which the feet appear to stick to the floor, is considered the characteristic gait disturbance. Dementia may not occur until late in the disorder. The most common early symptoms of dementia are disturbances of executive function and attention; memory tends to become impaired later.

The classic symptoms (gait disturbance, urinary incontinence, and dementia), even combined, are nonspecific for normal-pressure hydrocephalus, particularly in the elderly. For example, some forms of vascular dementia can cause dementia, gait disturbance, and, less commonly, urinary incontinence. Brain imaging may show ventricular enlargement disproportionate to cortical atrophy; this finding is nonspecific but may support the diagnosis of normal-pressure hydrocephalus.

Lumbar puncture with removal of 20 to 30 mL of CSF can be done as a diagnostic trial. Improvement in gait, continence, and cognition after such removal helps confirm the diagnosis and may predict the response to ventriculoperitoneal shunting, but the improvements may not be evident for several hours after CSF removal. In several case series (but in no randomized trials), significant improvement, typically in gait, continence, and daily functioning, occurred after shunting; improvement in cognition is less common.

Brain tumors: Rarely, primary or metastatic brain tumors cause dementia. Treatment consists of surgery, radiation therapy, or chemotherapy depending on the location and aggressiveness of the tumor.

This topic was last updated February 2006.