Somesthesia

Parkinson’s disease (PD) is, with good reason, conventionally considered a movement disorder. James Parkinson declared “the senses…uninjured” in the first paragraph of his monograph. However, many patients with PD do experience unpleasant sensations, and for some, these sensory symptoms are the biggest problem. The first segment of this chapter focuses on unpleasant somatic sensations occurring independent of or out of proportion to the cardinal motor symptoms. Pain as an extreme of dysesthesia is considered only briefly in this chapter and is treated more fully in the next chapter. Proprioception is the sense of the relative position of neighboring body parts, and kinesthesia, the sense of their relative motion. These senses, or at least the impact on the brain of their afferents from musculoskeletal tissues, appear to be defective in PD. Distortions of input and impaired processing of proprioception and kinesthesia may contribute to bradykinesia, dyskinesias, and postural instability, among other parkinsonian signs.