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Parallels Between AIDS Dementia and Parkinson's Disease
By Byron Young, M.D.

Clinical similarities between AIDS dementia and Parkinson's disease are currently being studied at the Kentucky Neurosciences Institute, in an effort to better understand the means by which the human immunodeficiency virus (HIV) affects the brain. Before death, approximately 30 percent of all HIV- infected persons will develop an overt dementing illness, evident on bedside neurological examination. This illness has been referred to as AIDS dementia. An additional 30 percent of HIV-infected persons will exhibit significant cognitive abnormalities that are evident only with detailed neuropsychological testing. On physical examination, these individuals often display abnormalities that are quite reminiscent of Parkinson's disease. In very rare instances, an older person infected with HIV may be misdiagnosed with Parkinson's disease until other AIDS-related illnesses become apparent.

Clinical Diagnosis

Among the most prominent findings in patients with AIDS dementia resembling Parkinson's disease are slow thinking (bradyphrenia), slow limb movements, altered gait, poor balance with frequent falls, stooped posture, increased muscle tone (rigidity), diminished facial expression, decreased eye blink rate, impaired smooth eye movements and abnormal speech. Additionally, patients may exhibit seborrheic dermatitis-a greasy, scaling rash often observed on the scalp, eyebrows and around the nose.

Clinical features which may prove helpful in distinguishing these patients from those with Parkinson's disease include the relative youthfulness of the HIV- affected population, the absence of a typical "pill-rolling" tremor of the extremities at rest (although a fine, fast tremor of the outstretched upper extremities is frequently observed), the presence of a fairly dramatic dementing illness from the onset of the illness, and the generally poor response to dopaminergic agents, such as levodopa. These patients often have an exquisite sensitivity to drugs that bind to the dopamine receptor or prevent its release. Small doses of such drugs, which include haloperidol, thorazine, metoclopropramide and reserpine, may leave a seemingly relatively unaffected individual bedridden due to increased limb and trunk rigidity.


HIV and Brain Infection

HIV infects the brain very early after the initial infection. It can be demonstrated in the brain within two weeks of infection, although it rarely causes clinically apparent disorders at this stage. The virus appears to have a predilection for deep nuclear structures, such as the basal ganglia, including the substantia nigra. This latter region of the brain is the region chiefly affected in Parkinson's disease. The infection appears to result in decreased numbers of neurons in this region and elsewhere. The content of dopamine (the neurotransmitter whose deficiency is critical in the development of Parkinson's disease) in the cerebrospinal fluid, as well as in the relevant, involved regions of the brain, is significantly depressed in comparison to controls. Positron emission tomography studies of the metabolism of these areas of the brain in affected individuals has revealed an initial hyperactivity of the basal ganglia early, followed in the late stages of the disorder by hypometabolism.


Research into AIDS Dementia

UK investigators are studying the activity of the basal ganglia in normal subjects and patients with AIDS dementia, using functional magnetic resonance imaging. In these studies, MRI is employed to measure blood flow of the basal ganglia, providing a measure of the metabolic activity of this region. When neurons in the basal ganglia are activated, as occurs with limb movement, the blood flow increases. Comparisons are possible of the degree of alteration from baseline assessment of neuronal activity in this region. These changes can be compared between normal individuals and HIV-infected persons with dementia and associated movement abnormalities. The effects of various therapeutic strategies that enhance dopaminergic activity will be assessed in the HIV study population to determine whether these agents have any potential in relieving the illness.

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