TABLE 5.
Markers of prodromal PD
| Marker | Level of evidence | Approximate relative risk | Lead time | Testing cost/burden |
|---|---|---|---|---|
| Olfaction | High | 5 | ?? | Low/Moderate |
| REM Sleep Behavior Disorder | High | 50 | 13 years | Low (screens) to High (PSG) |
| Somnolence | Moderate | 1.8 | ?? | Low |
| Restless legs (late onset) | Low | 1.5 | Short | Low |
| Constipation | High | 2.5 | > 15 years | Low |
| Orthostatic hypotension | Moderate | ? 2–10? | 2–5 years? | Low |
| Urinary dysfunction | Low-Moderate | 2.1 | ?? >5 years | Low |
| Erectile dysfunction | Low-Moderate | 1.2 mild 3.8 severe |
5–10 years | Low |
| Depression/anxiety | High | 1.8 | Uncertain ?Biphasic | Low, but follow-up higher |
| Color vision | Low | 2.5 | >3 years? | Moderate |
| Subtle parkinsonism | Moderate | 10 | 4–5 years | Moderate - High (Expert) |
| Quantitative motor testing | Moderate | 3–4 | 5 years | Moderate |
| SN ultrasound | Moderate | 15 | Uncertain ? risk marker? | Moderate-High |
| Dopaminergic PET/SPECT | Low (but high plausibility) | 20 | 5 years | High |
| PD-related pattern on SPECT/PET | Low | ? | ? | High |
| Hippocampal hyperperfusion | Low | ? | ? | High |
| GI synuclein pathology | Low | 2? | ? | High |
For this table, only markers with prospective evidence of predictive value are included. For level of evidence, low implies a single study, moderate implies >1 high-quality study, high implies >4 high-quality studies. Lead time refers to the approximate time that the marker deviates from normal values (the time at which testing is reliably abnormal cannot be estimated for most markers). For testing cost, low indicates can be screened by questionnaire (does not require visit), moderate implies in-person assessment required but low cost (eg, research assistant), high implies extensive or expensive evaluation (>$300).