Nearly 90% of individuals with Parkinson's disease (PD) develop voice and speech disorders during the course of their disease (1,2). These disorders are characterized by reduced voice volume (hypophonia); a breathy, hoarse, or harsh voice quality (dysphonia); imprecise consonant and vowel articulation due to reduced range of articulatory movements (hypokinetic articulation) and a tendency of these movements to decay and/or accelerate toward the end of a sentence; reduced voice pitch inflections (hypoprosodia, monotone); and rushed, dysfluent, hesitant, or stuttered-like speech (palilalia). Collectively, these disorders have been termed hypokinetic dysarthria (3). They may be among the first signs of PD, with hypophonia and dysphonia typically preceding articulation, prosodic and fluency disorders (1,2,4). Hypokinetic dysarthria in individuals with PD typically results in reduced speech intelligibility. Reduced facial expression (hypomimia) is also common in individuals with PD. Together, these can be interpreted as a person being cold, withdrawn, unintelligent, and moody (5,6). These factors may also impair the ability to socialize, convey important medical information, interact with family members, and maintain employment (5).
Nearly 90% of individuals with PD will also develop swallowing disorders (dysphagia) at some point (7). Dysphagia symptoms in PD include difficulty with lingual motility, reduced initiation of swallow, difficulty with bolus formation, delayed pharyngeal response, and decreased pharyngeal contraction (7-9). These symptoms are often accompanied by weight loss and lack of enjoyment of eating. Aspiration pneumonia is common, especially in the later stages, and can be a cause of death in PD (10).
Although neuropharmacologic and neurosurgical approaches have been shown to be effective in improving motor function of PD, their impact on voice, speech, and swallowing remains unclear (11). Traditional speech treatment of hypo-kinetic dysarthria has focused on rate, articulation, prosodic pitch inflection, and speaking in a louder voice, with only modest, short-lived therapeutic results (12,13). Swallowing treatment has focused on behavioral changes and diet modifications (9). A speech and voice treatment approach, known as the Lee Silverman Voice Treatment (LSVT®), has generated the first short- and long-term efficacy data (8,14,15) for suc cessfully treating voice and speech disorders in PD. The LSVT® has also been shown to improve tongue strength and motility (16), swallowing (8), facial expression (17), and brain function (18) in individuals with PD, but these research findings are preliminary.
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