Parkinsonian features: when are they Parkinson disease?

Parkinsonian syndromes can be classified into 2 major groups: Parkinson disease (PD)andatypicalparkinsoniandisorders. Commoncharacteristics includeakinesia, expressed as slowness and paucity of movement (eg, decreased arm swing or facial expression) and difficulty in initiating movement, and are associated with rigidity with or without resting tremor. Parkinsonian syndromes frequently occur in the elderly, their prevalence increasing markedly with age (14.9% at the age of 65 to 74 years; 52.4% at the age of 85 years or older).1 The most common parkinsonian syndrome, PD affects approximately one half million Americans. The incidence of PD is about 10 times that of atypical parkinsonian disorders.2,3 Diagnosis of PD was thought to be straightforward, but 3 recent large clinicopathologic studies showed that specialists misdiagnosed 25% to 40% of patients followed up in practice or assessed after reading detailed clinical vignettes.4-6 Misdiagnosis by nonspecialists is likely to be even higher. Early and accurate diagnosis is important because prognosis and treatment of patients with PD is markedly different from those for patients with atypical parkinsonian disorders. The survival of patients with early PD approximates that of the US population,7 particularlywhentheyaretreatedappropriately.8 Patients with any of the atypical parkinsonian disorders have shorter survival (usually ,10 years)9 and exhibit more frequent complications. Several clinical features help differentiate patients with early PD from those with atypical parkinsonian disorders. For instance, the presence of early autonomic dysfunction and of pyramidal or cerebellarsignshelpstodistinguishmultiplesystem atrophy (MSA) from PD, while early hallucinations,unrelatedtotreatment,and dementia support the diagnosis of dementiawithLewybodies.Tomakeanearlyand accurate diagnosis of these disorders, the clinician should evaluate the patient’s medicationandbladderhistory;bloodpressure;mental functions (includingapraxia); eyemovements;akinesia,rigidity, tremor, and writing (micrographia); and gait, posture, and postural stability. Although PD is chiefly a sporadic disorder, approximately 10% is familial. Familial PD usually has an earlier onset, more rapid progression, and other unusual features.