Saturday, August 16, 2008

Essentials of Diagnosis

• If caused by infection, the progression of dementia is over weeks to months rather than years.

• Frontal lobe abscesses may produce dementia without lateralizing or localizing signs.

• Creutzfeldt-Jakob disease should be considered in middle-aged patients with dementia that progresses over a few weeks.

Most dementing processes with infectious causes progress subacutely, that is, over weeks to months rather than over a course of years. A more slowly progressive course may be seen occasionally with communicating hydrocephalus, as a result of prior meningeal infection and interference with reabsorption of CSF. The dementia of tertiary syphilis may also progress over a very long time course.

Frontal Lobe Infections

Infections localized to the frontal lobes of the brain can present as dementias with few other manifestations. For example, a brain abscess in the frontal lobes may fail to produce lateralizing or localizing signs that would be obvious if the abscess were located elsewhere in the brain. Progressive multifocal leukoencephalopathy (PML) (see Chapter 45), even though a disease predominantly affecting the white matter can be present in the frontal lobes and produce dementia prior to the appearance of focal deficits. Although previously encountered as a rare complication of lymphoma or Hodgkin's disease, PML is now most often seen as a complication of AIDS. Dementia in AIDS is commonly seen in the late stages of the process, where it appears to be a direct result of the viral infection. The dementia is characterized by slowness of thought, apathy, and inability to perform consecutive tasks. Loss of motor functions with ataxia and spasticity are seen as the disease progresses. Dementia becomes increasingly frequent as AIDS progresses, with 50-75% of patients affected in the terminal course of the disease.

Creutzfeldt-Jakob Disease

In middle-aged patients with dementia progressing over a few weeks, one must consider the possibility of Creutzfeldt-Jakob disease, which appears to be a prion disease (Ferrer et al, 2000). The dementia in these patients often presents abruptly and worsens perceptibly every few days to weekly, evolving into a state of mutism within 2-5 months. Myoclonic jerking of limb and trunk muscles often accompanies the process, and the patients often startle easily. The electroencephalogram is always abnormal and sometimes may show a characteristic periodic burst-suppression pattern. The CSF is usually normal. An unusual protein has recently been described in the CSF of Creutzfeldt-Jakob patients, but its presence is not sufficiently specific to serve as a diagnostic test. Recently a few cases of Creutzfeldt-Jakob disease have been described in which MRI has demonstrated increased signal in the anterior striatum.

Although Creutzfeldt-Jakob disease, as it is seen sporadically, is not due to an infection, it is thought to result from a mutation in the prion protein gene with production of abnormal isoforms of normal prion proteins; these abnormal prion proteins, if transmitted into another human host, are infectious and, after prolonged incubation, cause the same disease in the recipient. Examples have been the occurrence of the disease in recipients of corneal transplants, dura mater grafts, and human-derived pituitary growth hormone after incubation periods of many months to many years. A variant form of the disease has recently appeared in Great Britain in young individuals, perhaps related to ingestion of beef from animals afflicted by "mad cow disease," another disorder related to infectious prions.


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