Parkinson's disease was first described by James Parkinson in 1817. It is a progressive neurodegenerative disease that affects almost one million Americans. About 60,000 new cases are diagnosed each year, and it typically occurs after the age of 60. As many as 40% of cases are thought to be associated with Parkinson's dementia; Parkinson's disease without dementia is sometimes described as Parkinsonism to make the distinction. The costs of care in the U.S. are estimated to be as much as $52 billion yearly.
Diagnosis depends on recognition of characteristic signs and associated symptoms such as resting tremor, bradykinesia, muscle rigidity, imbalance, shuffling gait, expressionless “mask” facial appearance, and non-extinguishing glabellar tap (Myerson's sign).
The distinction between Parkinson's disease and benign essential tremor should be straightforward. Benign essential tremor is characterized by intention (not resting) tremor; the amplitude of tremor is reduced by ambulation and suppressed by alcohol—features not found in Parkinson's disease—and the other characteristics of Parkinson's are absent. The differential diagnosis also includes other causes of dementia, especially Lewy body dementia, among several other less common conditions.
Accurate coding depends on complete, specific documentation, including the cause and any associated dementia. Parkinson's may be classified as primary or secondary; secondary causes include drugs and toxins, vascular disease (commonly with multiple micro-infarcts in the basal ganglia), and the aftereffects of encephalitis (which occurred most famously in the influenza pandemic of 1918). Antipsychotic medications are a common cause of secondary cases.
ICD-10-CM includes many different codes for Parkinson's disease that incorporate causes and the presence or absence of dementia (see Table). When dementia is associated with Lewy body dementia, the code for Lewy body dementia (G31.83) is assigned without a separate code for Parkinson's and a dementia code is added: F02.80 if without a behavioral disorder, F02.81 with a behavioral disorder.
ICD-10-CM allows coding of behavioral disorder without further clarification for any description of aggressiveness, combativeness, violence, or “wandering off.” Any other behavior that a clinician considers a behavioral disorder must be specifically stated as such.
When Parkinsonism occurs in patients with Huntington's disease, only the code for Huntington's is assigned. Parkinson's with neurogenic orthostatic hypotension (Shy-Drager syndrome) is assigned code G90.3 without any other code for Parkinson's.
The Table shows just how important a distinction between primary and secondary causes is; also make certain that the confirmed or suspected secondary cause is specified. If the patient also has dementia, identification of any behavioral disturbance is essential.
One other condition classified as Parkinson's disease by ICD-10-CM is neuroleptic malignant syndrome—a life-threatening neurologic emergency caused by antipsychotic drugs and characterized by a clinical syndrome of mental status change, muscle rigidity, fever, and autonomic dysfunction. It may also occur when levodopa or other dopamine agonist therapy is withdrawn, reduced, or changed to another agent. Code G21.0 is assigned for neuroleptic malignant syndrome and is the only code classified as a major complication/comorbidity in the Parkinson's group.
In summary, always indicate whether Parkinson's disease is primary or due to a secondary cause and clearly specify any confirmed or suspected secondary cause. Identify dementia when it occurs in association with Parkinson's, and clearly document the presence of any behavioral disturbances.