The presence of excessive saliva in the mouth with resultant drooling is a common problem in PD with estimates of up to 77% of patients being affected (31). When severe, patients will often complain bitterly about the problem and may request drug treatment to deal with it. Although the clinical impression of the physician is often that the patient has too much saliva, this turns out not to be the case. Proulx et al. (38) studied 83 PD patients and 55 controls by collecting saliva secreted over a five-minute period. They found that the PD patients secreted significantly less saliva than the normal controls and that levodopa use was a contributor to this reduced salivary output. It has also been demonstrated that de novo patients, not yet treated with dopaminergic drugs, have decreased salivary production (39). These studies suggest that although dopaminergic drugs may exacerbate the problem, decreased salivary production may be an early sign of autonomic involvement in PD.
If PD patients secrete less saliva than normals, why do they drool and appear to have excess saliva? The most likely explanation is that PD patients exhibit a decreased frequency of automatic swallowing, and when combined with a forward tilt of the head (common particularly in advanced PD), drooling results (38).
The treatment of drooling in PD has been attempted with anticholinergic drugs such as benztropine, scopolamine, and glycopyrrolate; the latter having been recommended as the agent with the fewest troublesome side effects (40). Most recently, several authors have reported results of botulinum toxin injections as a treatment for drooling in PD. Mancini et al. (41) injected 450 U of botulinum toxin type-A (Dysport®) into the parotid and submandibular glands using ultrasonographic guidance in PD and MSA patients with disabling sialorrhea. They reported a reduction of drooling within one week that lasted about a month and was unassociated with adverse effects such as dysphagia. Dogu et al. (42) compared ultrasound-guided botulinum toxin injections (Botox®) in the parotid gland with blind injections (using no guidance) and measured postinjection salivary output in the two groups. Although subjective sialorrhea improved in both groups, the group receiving ultrasound guidance experienced a significant reduction in salivary output, whereas the blind injection group did not. The authors concluded that ultrasound guidance is necessary to ensure success with botulinum toxin injections for this purpose. Ondo et al. (43) evaluated the effects of botulinum toxin type-B (Myobloc®) as a treatment for sialorrhea. In this study, ultrasound-guided injections with 2500 U of active drug was compared to placebo injections. Efficacy was evaluated by use of a visual-analog scale, questionnaires, and by salivary gland scintigraphy. The active drug group experienced significant improvement in all measures when compared with the placebo group. While there is considerable enthusiasm in the literature for various treatments for sialorrhea aimed at drying up saliva, it must be kept in mind that increased salivary production is not the problem in PD and that these patients already have reduced salivary output. Since saliva is an important component of oral health, drugs and procedures that reduce oral saliva may potentially lead to increased tooth decay (38). Although this has not yet been systematically studied, caution is required in the use of these agents.
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