Dementia is an acquired progressive cognitive impairment leading to interference with daily activities. Although Alzheimer’s disease is the most common cause of dementia in the elderly, dementia can be caused by several other neurodegenerative etiologies as well as vascular, infectious, toxic, metabolic, traumatic, neoplastic, or inflammatory causes.
The term dementia is derived from the Latin de (out of), men (mind), and tia (state of) and literally refers to a state of being out of one’s mind. When used currently, it refers to an acquired cognitive impairment involving multiple domains of function in the absence of a clouding of consciousness. During the past two decades, the concept of dementia has evolved from a unitary disease that describes a global cognitive impairment to its present use as an umbrella term for a number of distinctive disease entities. The recent development of symptomatic treatment options and the possibility of future treatments aimed at halting or reversing the disease processes have highlighted the importance of early and accurate diagnosis of specific dementia syndromes.
Although a large number of neurological diseases can cause dementia (Table 1), many of these are very rare. Alzheimer’s disease (AD) and vascular dementia account for most cases, especially in elderly populations. The relative frequencies of different dementia diagnoses are illustrated in Figure 1.
The most commonly used general diagnostic criteria for dementia are those proposed by the American Psychiatric Association in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV). These criteria define dementia as a syndrome consisting of progressive impairment in two or more areas of cognition (i.e., memory, language, visuospatial, reasoning and problem solving, and behavior) sufficient to interfere with work, social function, or relationships in the absence of delirium or major nonorganic psychiatric disorders. Below is a discussion for the possible treatable causes of dementia.
Treatable Causes of Dementia
Normal Pressure Hydrocephalus
Normal pressure hydrocephalus (NPH) often presents with the classical triad of cognitive impairment, urinary incontinence, and gait apraxia with associated significant ventricular enlargement out of proportion with cortical atrophy on imaging studies. The cognitive profile is one of marked slowing, and the apraxia is virtually confined to gait with the characteristic glued-to-the-floor ‘magnetic’ gait. The etiology in many cases is unclear, although some are secondary to head injury, subarachnoid hemorrhage, or meningitis. Although many patients with NPH respond to removal of cerebrospinal fluid at lumbar puncture, predicting which patients will respond to ventricular shunting procedures is far from reliable with MRI, and intracranial pressure monitoring fails to reliably predict outcome.
Chronic Subdural Hematoma
Chronic subdurals often present subacutely with a fluctuating level of consciousness, symptoms of increased intracranial pressure, and often focal signs. They commonly occur in individuals prone to falls, such as alcoholics, the elderly, and those with coexistent neurological conditions. Treatment is by surgical evacuation of the hematoma, although many recur.
Metabolic and Endocrine Disturbance
Many metabolic disturbances, such as hyponatremia, renal, or hepatic failure, may cause cognitive symptoms, although the features are usually more typical of delirium than dementia. Disease of the thyroid is common, especially in the elderly population, but dementia due to hypothyroidism is rare and most reported cases have been shown to have developed AD on follow-up. More commonly, hypothyroidism will present with cognitive symptoms associated with depression and psychomotor retardation.
There is increasing awareness of a group of inflammatory cognitive disorders known as autoimmune encephalopathies. These have gone by various other names including nonvasculitic autoimmune inflammatory meningoencephalitis. One such condition is Hashimoto’s encephalopathy, a condition of cognitive dysfunction and seizures associated with high concentrations of antithyroid antibodies, often with normal or near normal thyroid function. Other antibody-mediated encephalopathies may be paraneoplastic, or associated with an underlying malignancy.
Vitamin B12 deficiency is the most commonly encountered deficiency state and is usually associated with pernicious anemia. The most frequent neurological features are spinal cord dorsal column damage and peripheral neuropathy. Cognitive features are less common and usually present as hypoactive delirium, confusion, or psychomotor retardation rather than dementia. Replacing B12, especially if the duration of symptoms is short, can improve cognitive deficits at least in part.
Infection of the central nervous system by the human immunodeficiency virus (HIV) is probably the most common cause of dementia in the young. Also known as the acquired immune deficiency syndrome dementia complex, HIV-associated dementia presents as a subcortical dementia with psychomotor slowing, memory disturbance, apathy, withdrawal, and associated spastic gait disorder and hyperreflexia. Because it is usually a late manifestation of HIV infection at a stage when opportunistic infection or neoplasms may be prevalent, investigation should be directed at excluding focal lesions such as toxoplasmosis, cryptococcal meningitis, cytomegalovirus encephalitis, diffuse infiltration by lymphoma, and progressive multifocal leukoencephalopathy. Treatment with antiretroviral agents has been shown to improve cognitive deficits.
This excerpt was taken from the chapter Dementia in the article by D. C. Perry from the Multi-Volume Reference Work Encyclopedia of the Neurological Sciences (Second Edition). The easy-to-use ‘encyclopedic-dictionary’ format of this four-volume set features alphabetic entries, extensive cross-referencing, and a thorough index for quick reference. The wealth of information provided makes this reference work a trusted source of valuable information for a wide range of researchers, from undergraduate students to academic researchers.