Pain in Parkinson's Disease.

Pain is reported by nearly 50% of patients with Parkinson's disease. In some patients, it can be more debilitating than the motor deficits. In order to identify the appropriate treatment strategy for each patient, it is useful to categorize pain syndromes as follows: 1) low DOPA (end of dose wearing off, diphasic, or early morning) painful states are associated with inadequate levels of dopamine receptor stimulation; 2) high DOPA (peak dose) painful states occur at times of maximum levodopa efficacy; and 3) many patients report pain that has no obvious relation to dopaminergic medications or may even be caused by other conditions. Low DOPA painful states are best treated by trying to provide more continuous dopaminergic stimulation and thereby reduce or prevent the number and duration of "off" periods. Adding or increasing the dose of direct-acting dopamine receptor agonists or of catechol-o-methyl transferase inhibitors is the best first-line strategy. Other approaches include increasing the frequency of immediate-release levodopa preparations or using controlled-release preparations. More invasive approaches should be considered only when simpler methods fail. These include deep brain stimulation to the pallidum or the subthalamic nucleus, or direct duodenal continuous infusion of levodopa in patients who are unable to undergo surgery. Pain associated with excessive dopaminergic stimulation usually is a result of dystonia or severe chorea. Reduction of levodopa is the first step in attempting to diminish high DOPA states, followed by reduction or cessation of other dopaminergic agents such as selegiline, catechol-o-methyl transferase inhibitors, or direct-acting dopamine receptor agonists. Adding amantadine can reduce chorea significantly and it should be tried if the potential and actual side effects are tolerable to the patient. Deep brain stimulation is a good final option if medication adjustments are ineffective. Nonspecific pains of Parkinson's disease can be difficult to treat. The effective use of central pain suppressant or analgesics is anecdotal and difficult to verify. In untreated early disease, generalized pain or pain related to joint or muscle immobility may be reduced by effective treatment of the underlying Parkinson's disease.