Table 1.

Biomarkers of PD at various stages.

	Prodromal PD	Preclinical PD	Clinical PD
Clinical status	Starts with early non-motor symptoms along with early subtle motor symptoms and PD pathology is present.	No clinical signs or symptoms.	Classical motor manifestations are present.
Biomarkers	Non-motor symptoms Hyposmia (olfactory deficits) Visual abnormalities (oculomotor disturbances). Neuropsychiatric symptoms i. Depression ii. Anxiety iii. Anhedonia iv. Orthostatic hypotension v. Sleep disorders such as REM-sleep behavior disorder vi. Constipation and other dysautonomic Features. vii. Urogenital dysfunction. viii. Mood disorders and neurobehavioral abnormalities	Molecular imaging DAT SPECT Florodopa PET scan Transcranial sonography Magnetic resonance imaging Optical resonance tomography Biochemical biomarkers Genetic biomarkers	Motor symptoms Akinesia Bradykinesia Hypokinesia Postural instability Rigidity Stooped posture Tremor at rest Gait impairment Stiffness of arms, legs, trunk Poor balance and co-ordination