Major or Mild Neurocognitive Disorder Due to Parkinson’s Disease 637
lowed by 294.10 (F02.80)  major neurocognitive disorder probably due to Parkinson’s dis-
ease, without behavioral disturbance.
For major neurocognitive disorder possibly due to Parkinson’s disease, code 331.9
(G31.9)  major neurocognitive disorder possibly due to Parkinson’s disease. ( Note:  Do not
use the additional code for Parkinson’s disease. Behavioral disturbance cannot be coded
but should still be indicated in writing.)
For mild neurocognitive disorder due to Parkinson’s disease, code 331.83 (G31.84).
(Note:  Do not  use the additional code for Parkinson’s disease. Behavioral disturbance
cannot be coded but should still be indicated in writing.)
Diagnostic Features
The essential feature of major or mild neurocognitive disorder (NCD) due to Parkinson’s
disease is cognitive decline following the onset of Parkinson’s disease. The disturbance
must occur in the setting of established Parkinson’s disease (Criterion B), and deficits must
have developed gradually (Criterion C). The NCD is viewed as probably due to Parkinson’s
disease when there is no evidence of another disorder that might be contributing to the
cognitive decline and when the Parkinson’s disease clearly precedes onset of the NCD. The
NCD is considered possibly due to Parkinson’s disease either  when there is no evidence of
another disorder that might be contributing to the cognitive decline or when the Parkin-
son’s disease precedes onset of the NCD, but not both.
Associated Features Supporting Diagnosis
Frequently present features include apathy , depressed mood, anxious mood, hallucina-
tions, delusions, personality changes, rapid eye movement sleep behavior disorder, and
excessive daytime sleepiness. 
Prevalence