Nonpharmacological Management of Hypokinetic Dysarthria in ParkinsonÂ’s Disease

AM Johnson, PhD; SG Adams, PhD


Geriatrics and Aging. 2006;9(1):40-43. 

In This Article

Abstract and Introduction

In addition to its widely recognized effects on gait, posture, balance, and upper limb coordination, Parkinson's disease (PD) can have a profound effect on speech and voice, within a cluster of speech characteristics termed hypokinetic dysarthria. Although dopaminergic therapy produces significant benefits in the early stages of PD, speech symptoms may show selective resistance to pharmaceutical therapy in patients with a disease history of more than 10 years. This article discusses the pathophysiology of PD as it relates to speech disorders and considers nonpharmaceutical therapeutic options for hypokinetic dysarthria.

Parkinson's disease (PD) is a degenerative illness whose cardinal symptoms include rigidity, tremor, and slowness of movement.[1] In addition to its widely recognized effects on gait, posture, balance, and upper limb coordination, PD can have a profound effect on speech and voice. Although symptoms vary widely from patient to patient, the speech symptoms most commonly demonstrated by patients with PD are reduced vocal loudness, monopitch, disruptions of voice quality, and abnormally fast rate of speech. This cluster of speech symptoms is often termed hypokinetic dysarthria.[2] While dopaminergic medications are typically effective in treating the voice or speech symptoms that present in the early stages of the disease,[3] some research has suggested that these symptoms may become selectively resistant to pharmaceutical treatment in the latter stages (10+ years) of the disease.[4] Despite the fact that some 60-80% of patients with PD may be expected to develop some voice or speech symptoms,[5,6] it has been estimated that only four percent of these patients receive speech therapy.[7] In this article, we will review the putative pathophysiology of PD as it relates to voice and speech disorders and discuss current trends in the nonpharmaceutical treatment of these symptoms.

The most common symptom of hypokinetic dysarthria is hypophonia, or reduced vocal loudness. Patients demonstrating this symptom may be unaware of the volume at which they are speaking and may require frequent requests to speak louder. Hypokinetic dysarthria also manifests as a lack of variability in pitch or loudness, wherein a patient may demonstrate monopitch, monoloudness, or reduced use of conversational inflection. Similarly, patients with PD often have disruptions of voice quality, in which their voice takes on an abnormal breathiness or hoarseness. Finally, hypokinetic dysarthria can, paradoxically, result in an abnormally fast rate of speech—not unlike the festination of gait that is often a symptom of PD. While it is difficult to attribute these symptoms to specific biological determinants, the pathophysiology of PD is specifically related to speech function in a number of key areas, most notably respiratory or aerodynamic function, laryngeal abnormalities, and motor control.[3]

PD seems to produce a consistent impairment of respiratory function. This impairment takes the form of an overall reduction in function[8] and an increased variability in air flow.[9] Although early research suggested that these abnormalities were caused by reduced movement of glottic and supraglottic structures,[9] more recent research has suggested that they may be more related to irregularities in muscle activation patterns within the chest wall[10] or reduced expansion of the rib cage.[11] Impairment of respiratory function has been implicated strongly in hypophonia and is targeted accordingly by many speech therapy paradigms.

While there are few data on the laryngeal abnormalities of patients with PD, the classic pathophysiology of hypokinetic dysarthria includes dysfunction of vocal fold kinematics[12] (i.e., slow opening and inadequate closing of the vocal folds), vocal fold asymmetry and bowing,[13] and vocal fold paresis.[14] These physiological changes may be responsible for much of the vocal hoarseness and hypophonia seen in hypokinetic dysarthria. It has also been suggested that, in some patients with PD, vocal hoarseness may result from dyskinesia within the laryngeal system.[15]

Given the primarily motoric sequelae of PD, it is not surprising that motor control has been implicated in speech dysfunction. As aforementioned, motor control deficits are related to speech breathing in PD.[10,11] Impaired motor control has also been shown to reduce the speed and amplitude of both jaw movements[16] and lip movements.[17] While it has been hypothesized that reduced amplitude of oral movements is the primary cause of reduced speech intelligibility in PD, the studies required to clearly establish this causal link are still lacking.[3,18]