Parkinson disease is a progressive neurodegenerative disorder with significant morbidity and mortality. Approximately 60,000 people are diagnosed with Parkinson disease each year in the United States; it is the 14th leading cause of death, with most patients dying from complications of the disease.¹ Most patients consult with their primary care physician about Parkinson disease symptoms before seeking care from a specialist. Primary care physicians are often the most accessible to patients and caregivers coping with this disease.

Pathophysiology

Parkinson disease is characterized by a progressive loss of dopamine-producing neurons in the basal ganglia, particularly in the substantia nigra,² and development of Lewy bodies in the dopaminergic neurons. Lewy bodies are the pathologic feature of Parkinson disease.³ However, Lewy bodies are nonspecific for Parkinson disease and are found in multiple neurodegenerative diseases; therefore, Parkinson disease represents a disease syndrome with different clinical subtypes.⁴

Diagnosis

The diagnosis of Parkinson disease is clinical, and key features include bradykinesia, rigidity, and tremor. The most common presenting symptom in Parkinson disease is a unilateral resting tremor, often localized to the distal muscles of the hand, causing a pill-rolling motion. Some patients note an internal tremulousness sensation before the manifestation of the pill-rolling tremor.⁵ Rigidity usually starts on the side of the body affected by the tremor and can affect gait, contribute to muscle pain, and impair posture. Cogwheel rigidity, in which affected muscles ratchet or alternate rapidly between rigidity and relaxation when moved passively, is the most common type in Parkinson disease. A small number of patients with Parkinson disease present with lead pipe rigidity, in which affected muscles stay rigid throughout the passive motion.

The main diagnostic signs of Parkinson disease are motor symptoms; however, nonmotor symptoms are also common and debilitating. Nonmotor symptoms that often present before motor symptoms include rapid eye movement sleep disorder, depression, constipation, fatigue, and olfactory dysfunction. A large survey of patients with Parkinson disease found that almost all patients reported nonmotor symptoms, with psychiatric symptoms occurring most often.⁶ Associated nonmotor symptoms that can occur later in the disease can include autonomic dysfunction such as orthostatic hypotension and urinary dysfunction, which can impact quality-of-life and level-of-care issues for patients. Some nonmotor symptoms such as dementia and psychosis occur with advanced Parkinson disease but are notably debilitating.

A physical examination should include assessment for decreased spontaneous or uncontrollable movements, tremors, or flat or masked facial expressions. A gait examination should assess for shuffling gait, stooped posture, en bloc turns, freezing (i.e., sudden transient arrests of movement), or postural instability. Bradykinesia, or the overall slowing of movement, includes decreased manual dexterity, shuffling steps, freezing gait, and festinating gait (i.e., involuntary gait acceleration). For a video illustrating common Parkinson disease movements, see https://www.youtube.com/watch?v=pFLC9C-xH8E. The neurologic examination should focus on muscle tone (e.g., cogwheel, lead pipe) and bradykinesia through rapid alternating movements testing.

Misdiagnosis often occurs because of the multiple symptoms associated with Parkinson disease and the notable clinical overlap with other diseases. Careful examination of the tremor can differentiate between Parkinson disease and other causes. Whole hand tremor is usually an essential tremor or it can be attributed to cerebellar causes. Features supporting a diagnosis of Parkinson disease are asymmetric clinical motor presentation, gradual onset, and bradykinesia. Motor symptom response to levodopa also supports the diagnosis. Insidious progression of symptoms and postural instability are hallmarks of later stages of Parkinson disease. Factors indicating another diagnosis are rapid disease progression, early or symmetric bilateral body involvement, and inadequate response to levodopa.⁷ Although upper extremity tremor is the more common presenting symptom in Parkinson disease, the development of lower extremity tremor favors a diagnosis of Parkinson disease over essential tremor.^8,9 Essential tremor, progressive supranuclear palsy, drug-induced parkinsonism, and Lewy body dementia are often mistaken for Parkinson disease.