Which neurologic disorders are associated with taste and smell disorders?

Updated: Jan 08, 2021
  • Author: Eric H Holbrook, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Degenerative processes of the central nervous system (eg, Parkinson disease [PD], Alzheimer disease) and other neurologic diseases (Huntington disease, multiple sclerosis, motor neuron disease) have been associated with hyposmia. Patients with Alzheimer or Parkinson disease show changes in detection, discrimination, and identification of odors compared with age-matched controls. The severity of dysfunction is correlated to disease progression, although in most cases, olfactory loss is present years before motor or cognitive symptoms; this is usually a gradual loss and often goes unnoticed or unreported by patients.

The presence of olfactory dysfunction at the time of PD diagnosis increases the risk of developing dementia. [27] Indeed, in general, olfactory loss in an individual increases the odds of being diagnosed with dementia within 5 years, [28] but this may be a phenomenon of an overall association of age-related sensory impairment with cognitive impairment. [29]

A study by Roos et al, using the University of Pennsylvania Smell Identification Test, the Unified Parkinson’s Disease Rating Scale motor subscale, and the Mini-Mental State Examination, reported a relationship between hyposomia and motor and nonmotor symptoms of PD, including with regard to cognition, depression, anxiety, autonomic dysfunction, and sleep disturbances. It was also linked to the degree to which nigrostriatal dopaminergic cells are lost. In addition, using single-photon emission computed tomography (SPECT) scanning, the investigators found that olfactory test scores were strongly associated with the binding of dopamine transporter in the putamen and caudate nucleus. [30]

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