Biomedical subjects
Publications and source records attributed to D B Calne.
The cerebrospinal fluid concentration of hydroxylase cofactor has been measured in patients with Parkinson's disease, the Shy-Drager and Steele-Richardson syndromes, adult onset focal dystonia, essential tremor, Huntington's disease and presenile dementia. The results were compared with age matched controls and low values were demonstrated for all disease groups studied except for focal dystonia.
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Over the last two decades there have been spectacular advances in understanding and treating Parkinson's disease, but there remain major areas of uncertainty and ignorance. The nigrostriatal pathway has features resembling the peripheral sympathetic system, rather than conventional central projections of sensory and motor nuclei. Like sympathetic activity, nigrostriatal function is diffuse, tonic, and more accessible to analysis by measuring biochemical rather than electrical changes. These findings are difficult to interpret in the context of the established importance of the basal ganglia in programming movement. The role of the depletion of dopamine in Parkinsonism is also unclear; we do not even know whether the impact of the deficit is more significant in the basal ganglia, or the substantia nigra. Confusion over the actions of dopamine underlies the obscurity of the mechanisms by which levodopa produces both wanted and unwanted effects. Finally, the nature of Parkinson's disease is still an enigma: we have not identified its cause, and we do not know what influences its progress.
A method for measuring hydroxylase cofactor activity in human cerebrospinal fluid is described. The hydroxylase cofactor content of cerebrsopinal fluid from Parkinsonian patients is approximately 50 percent that of normal subjects. A significant correlation between hydroxylase cofactor and the concentration of homovanillic acid in the cerebrospinal fluid was observed.
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Continuous intravenous infusion of levodopa was used for eight days to manage a parkinsonian patient with "on-off" fluctuations who underwent abdominoperineal resection for carcinoma of the rectum. Reasonable control of parkinsonism was obtained initially with small doses of levodopa, but more than 4 g daily were eventually required. No adverse effects on cardiac rhythm, blood pressure, or gastrointestinal function occurred. Frequent adjustment of levodopa dosage was necessary in view of continuing "on-off" fluctuations. Severe akinesia, which can cause dysphagia, respiratory complications, and venous stasis in the legs, can benefit from this method of management after major abdominal surgery in a patient with advanced parkinsonism.
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Because of the high concentrations of gamma-aminobutyric acid (GABA) in the cerebellar cortex and nuclei, an attempt was made to enhance GABAergic transmission in patients with cerebellar disease. Maximum tolerated doses of sodium valproate, a drug which inhibits the degradation of GABA, failed to influence cerebellar deficits in a double blind crossover study on six patients.
Because there is biochemical evidence of decreased GABAergic function in Parkinson's disease, sodium valproate, an inhibitor of GABA catabolism, was administered to eight Parkinsonian patients. Valproate treatment did not significantly alter any Parkinsonian feature, but tended to increase the dyskinesia in the "on-off" patients. The increased dyskinesias were not a result of altered peripheral metabolism of L-dopa. Despite obtaining high plasma levels of valproate, no consistent alteration of CSF GABA levels could be demonstrated. Thus, in these patients, an effect of valproate on GABA metabolism is unproven, and in turn, the role of GABA in Parkinsonism and dyskinesia uncertain.
While the era of major advances in understanding and treating parkinsonism seems to be over, steady progress is being made in elucidating physiological and pharmacological aspects of extrapyramidal function. The dramatic impact of levodopa therapy has been followed by the recognition of serious limitations to its long-term use, which provides a continuing stimulus for efforts to analyze the physiological and pharmacological properties of the basal ganglia and substantia nigra. There are reasonable grounds for the hope that this research will lead to significant developments in therapy.
Eight out of 12 unselected patients with Shy-Drager syndrome were found to have severe bilateral paresis of vocal cord abduction by fibre-optic laryngoscopy. This commonly presented as increased snoring followed by episodes of inspiratory and expiratory stridor and sometimes by sleep apnoea. Respiratory failure eventually developed in four cases and was reversed by tracheostomy. In another patient tracheostomy relieved severe attacks of sleep apnoea. This complication was not necessarily associated with advanced disease, and it should be considered in all patients with Shy-Drager syndrome as appropriate treatment can lead to a useful extension of life.
Two recent sporadic cases of progressive Parkinsonism after encephalitis are described. Both patients had two oligoclonal protein bands in their CSF. These bands were not present in patients with idiopathic Parkinson's disease and might, therefore, be useful for diagnostic purposes, particularly when the history of encephalitis is uncertain.
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Advances through basic research have elucidated the disturbances of neurotransmitter function in Parkinson's Dopamine has replaced acetylcholine and norepinephrine as the most studied neurotransmitter, with both conceptual and practical developments, exemplified by the hypothesis of cyclic adenosine monophosphate as a "second messenger," and new therapeutic agents. We now have rationally designed in-vitro and in-vivo tests for the evaluation of dopaminergic compounds instead of entirely empiric screening procedures. We are starting to identify different categories of dopaminergic receptors and to manipulate them selectively, with gains in understanding the physiologic input to the striatum. Crucial questions remain, including how dopamine modulates striatal output and what causes the parkinsonian degeneration of the nigrostriatal pathway. Developing knowledge on synaptic physiology and pharmacology may lead to better therapy.
Increased serum activities of the enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST) occurred in 12 out of 19 patients with idiopathic parkinsonism when they were treated with the ergot derivative lergotrile at an oral dose varying from 50 to 150 mg daily. Hepatocellular injury was confirmed by microscopic examination of liver biopsies obtained from 3 of these patients when the serum activities of ALT and AST were appreciably elevated. Light microscopy revealed features of mild acute hepatocellular injury, and electron microscopy showed proliferation of the smooth endoplasmic reticulum and apparently unique mitochondrial changes in hepatocytes. This is the first report of pathological changes in the liver associated with the therapeutic use of an ergot derivative. The presence of a potentially reactive cyanide group in the lergotrile molecule could be causally related to the observed hepatocellular injury. It is suggested that serum ALT and AST activities should be monitored carefully when the therapeutic potential of any new ergot derivative is assessed.
The response of Parkinsonism to three ergot derivatives which modify dopaminergic transmission was studied. CF 25-397 behaved more as an antagonist than an agonist. Lergotrile was an agonist with therapeutic properties marred by prominent hepatotoxicity. Bromocriptine is an effective anti-Parkinsonian agent, particularly useful in patients with prominent dyskinesia or "on-off" reactions to levodopa; in most patients optimal results have been obtained by combining from 40 to 90 mg of bromocriptine daily with approximately 60% of the previous maximal dose of levodopa. Unfortunately, only some 50% of patients tolerate long-term bromocriptine therapy, but all adverse reactions have been dose dependent and reversible.
92 patients with parkinsonism have been treated with bromocriptine for up to 30 months. 48 continue to receive bromocriptine with benefit; of these, 35 take bromocriptine (mean dose 53 mg daily) in combination with levodopa and 13 take bromocriptine (mean dose 45 mg daily) without levodopa. In those who were originally on levodopa, addition of bromocriptine allowed a mean 41% reduction in the dose of levodopa; the largest group of patients to benefit from bromocriptine entered the study because of excessive dyskinesia or "on-off" phenomena induced by levodopa. In 40 patients bromocriptine was stopped because of adverse reactions, absence of therapeutic response, or non-compliance with the protocol. The main problems were psychiatric disturbance (8 patients) and erythromelalgia (7 patients); these effects tended to occur late (mean 6 months and 10 months, respectively) and with high dosage (mean 66 mg and 115 mg daily). Other frequent adverse effects were dizziness and nausea; these began considerably earlier (at 2 months and 1 month) and with much lower dosage (31 mg and 12 mg daily). 4 patients died, for reasons apparently unrelated to therapy.
Animal experiments suggest that opiate peptides might play a role in extrapyramidal function. This hypothesis was tested by administering the opiate antagonist, naltrexone, in doses sufficient to antagonize exogenous opiates, to patients with parkinsonism and Huntington's disease. No improvement in the clinical features of either disorder was noted.