Olfaction as a Biomarker in Parkinson's Disease

Parkinson’s disease (PD) was first described by James Parkinson in 1817 in his thesis work, which he first noticed in the people of London. Today, the disease affects 1–2% of the population, who is more than 65 years of age. 1 PD is now recognized as a spectrum of alpha synuclein and tau related disorder. 2 Apart from major cardinal motor manifestations of bradykinesia, rigidity, rest tremor and postural instability, it has many non motor features such as altered smell, taste, vision, sleep, bladder and bowel dysfunction, cardiovascular abnormality, salivation, mood and cognition. 2 , 3 Olfactory dysfunction occurs in more than 90% of PD patients, and it often precedes the motor manifestation for years, marking its importance and it easily exceeds the cardinal motor manifestation of tremors (75%). 4 Though the loss of smell is not complete in 80% of patients, most subjects fail to recognize olfactory loss until tested. 4 Until 1980s not much investigatory tools were available for detecting olfactory dysfunction, and hence it hardly drew any attention. After University of Pennsylvania Smell Identification Test (UPSIT) was developed, several authors have shown olfactory dysfunction in PD patients. 5