Neurology and psychiatry
Many neurological conditions may present with cognitive impairment or psychiatric symptoms. Those conditions which are usually dealt with by neurologists or neuropsychiatrists are discussed below. Those which are usually dealt with by old age psychiatrists (i.e. Alzheimer’s disease, vascular dementia, Lewy body disease and Pick’s disease) are discussed on pages 90–91, along with a description of the management of dementia. The principles of management discussed on page 91 are just as applicable to the causes of dementia described below
Creutzfeldt–Jakob disease (CJD)
This rare infective form of dementia is the most common human form of the spongiform encephalopathies, so-called because of the sponge-like appearance of the brain at postmortem. It is caused by transmission of an abnormal prion protein that is found in plaques in the brain of affected cases. The risk of contracting CJD is thought to depend on the extent of exposure to the abnormal prion protein and genetic susceptibility factors in the exposed person. Following infection, it may be several decades before dementia develops, as evidenced by the adult-onset of dementia in people who had been treated with contaminated human growth hormone during childhood. Variant CJD (vCJD) is a new disorder, first described in 1996, and is strongly linked to exposure to beef products that have been infected with bovine spongiform encephalopathy (BSE). Some of the issues concerning transmission of CJD and other spongiform encephalopathies are summarised in Figure 1.
CJD can present initially with psychiatric symptoms, especially depression and anxiety, but rapidly progresses to a severe dementia associated with neurological deficits that include pyramidal, extrapyramidal and cerebellar signs. There is a characteristic triphasic pattern on EEG.
Huntington’s disease
This condition is also known as Huntington’s chorea. It is caused by an abnormal trinucleide repeat on chromosome 4 which is inherited in an autosomal dominant fashion. The mean age of onset is in the fifth decade, with age of onset being inversely correlated with the length of the abnormal trinucleide repeat. There is marked neuronal degeneration in the frontal lobes and basal ganglia, especially the caudate nucleus. The mechanism by which the genetic abnormality causes this neuropathology is unknown.
The three main groups of symptoms are choreiform movements, dementia and psychiatric symptoms. The onset of these different symptoms can be several years apart and diagnosis may be difficult if choreiform movements are not the first symptoms to appear. The choreiform movements are sudden, involuntary movements which initially affect the face and shoulders, appearing like a mild twitch or shrug. They progress into severe writhing movements associated with ataxia. Dementia usually occurs late in the course of illness and memory and insight are relatively well preserved compared with other cognitive functions. Psychiatric symptoms occur at an early stage and are often the first to present. Depressive symptoms are most common and mania and paranoid psychosis also occur.
Genetic testing
Children of patients with Huntington’s disease have a 50% chance of developing the condition themselves. Using genetic probes, it is now possible to determine whether family members carry genetic markers on chromosome 4 which are associated with the disease. However, as nothing can be done to stop the disease developing, many relatives choose not to be tested. Prenatal testing is also possible, though it is important to remember that a positive test in a fetus implies that the parent at risk will go on to develop the disease.
Parkinson’s disease
Depression occurs in up to 40% of cases of Parkinson’s disease. This is a higher rate than in conditions that cause a similar amount of disability, suggesting that changes in brain structure or function contribute to the depression. There is also a raised risk of dementia in patients with Parkinson’s disease, with many cases probably caused by Lewy body disease (p. 90).
Multiple sclerosis
Cognitive impairment may develop at any stage of the illness. Dementia is usually a late complication but eventually develops in up to 50% of patients. Psychiatric symptoms are even more common, with one-third of patients developing depressive episodes and nearly all patients experiencing depressive and anxiety symptoms at times. This is not surprising considering the enormous psychosocial impact of having multiple sclerosis. Lesions in the brain may also contribute to depressive mood changes, and are nearly always the cause of the euphoric mood which occurs in up to 10% of patients.
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