Parkinson disease is due to a degeneration of neurons in the dopaminergic nigrostriatal pathway. It is the second most common movement disorder behind essential tremor. Cardinal manifestations include bradykinesia, rigidity, tremor, an expressionless face, and postural instability. Asymmetry is characteristic. The disease often begins asymmetrically; the signs may be so lateralized as to warrant the designation of hemi-PD, and some asymmetry usually persists even when the disease is well established. The major manifestations vary from case to case.

Parkinson disease causes marked hypertonia, or rigidity, which principally affects the axial muscles and the proximal and flexor groups of the extremities, causing an increased tone to passive movement. The rigidity has a rhythmic quality referred to as cogwheel rigidity, presumably due to the superimposition of the tremor. Cogwheeling may be brought out as the examiner passively moves an elbow or wrist by having the patient grit the teeth, look at the ceiling, or use the opposite hand to make a fist, trace circles in the air, or imitate throwing a ball. The rigidity is present evenly throughout the range of movement, without the ebb at the extremes of the range that occurs in spasticity.

In PD, there is a paucity of movement and a slowing of movements. Strictly speaking, akinesia means an absence of movement, bradykinesia a slowness of movement, and hypokinesia a decreased amount or amplitude of movement, but the term bradykinesia is often used to encompass all three. There is loss of associated and automatic movements, with masking of the face, infrequent smiling and blinking, and loss of swinging of the arms in walking (Figure 21.1).

Patients with PD have poor balance, a tendency to fall, and difficulty walking. The gait abnormality is stereotypical: slow and shuffling with a reduced stride length, sometimes markedly so, a stooped flexed posture of the body and extremities, reduced arm swing, and a tendency to turn “en-bloc.” Impaired postural reflexes lead to a tendency to fall forward (propulsion), which the patient tries to avoid by walking with increasing speed but with very short steps, the festinating gait. Falls are common. If a patient, standing upright, is gently pushed either backward or forward, she cannot maintain balance and will fall in the direction pushed. Facial immobility and lack of expressiveness is a common feature of PD (hypomimia, masked face). A decreased rate of blinking, accompanied by slight eyelid retraction, causes patients to have a staring expression (reptilian stare). The voice is typically soft, breathy, monotonous, and tremulous. Other common manifestations include hyperhidrosis, greasy seborrhea, micrographia, somnolence, difficulty turning over in bed, blepharospasm, and apraxia of eyelid opening. Oculogyric crisis, forced involuntary eye deviation, usually upward, is a feature of postencephalitic PD and can occur in drug-induced parkinsonism, but it does not happen in idiopathic PD. Other common manifestations include foot dystonia, “striatal toe,” an exaggerated glabellar tap reflex (Myerson sign), and impaired handwriting (especially micrographia). Advancing disease is characterized by increasing gait difficulty, worsening of tremor and bradykinesia, motor fluctuations related to levodopa therapy, behavioral changes, cognitive impairment, hallucinations, intractable drooling, and sleep impairment. The impairment of cognition in PD is extremely variable, ranging from minimal involvement to profound dementia. Some degree of cognitive blunting may occur in 20% to 40% of patients. Early, prominent, and nonvisual hallucinations raise the possibility of dementia with Lewy bodies.

The diagnosis of PD is predominantly clinical, and differential diagnosis essentially is between other conditions causing tremor, of which essential tremor is the commonest, and other akinetic-rigid syndromes. Clinical features that favor PD include prominent rest tremor, asymmetric signs, preservation of balance and postural reflexes in the early stages of the disease, and a good response to levodopa replacement therapy. The other degenerative disorders with parkinsonian features typically produce other neurologic signs, such as gaze limitation, cerebellar signs, pyramidal signs, severe dementia, apraxia and other parietal lobe signs, or dysautonomia, although these other manifestations may not be apparent early in the course. Certain drugs can induce a reversible condition that mimics PD. The most common agents that cause drug-induced parkinsonism are antipsychotics, especially the high-potency piperazine compounds such as haloperidol. Some of the other conditions important in the differential diagnosis of PD include multiple system atrophy, progressive supranuclear palsy, corticobasal degeneration, and diffuse Lewy body disease.

Wilson disease (hepatolenticular degeneration) is a rare, autosomal recessive disorder due to abnormal copper deposition in the brain. The usual age of onset is between the ages of 10 and 20, and major manifestations include tremor, rigidity, dystonia and abnormal involuntary movements of various types, dysarthria, dementia, parkinsonian features, spasticity, cerebellar signs, and psychiatric abnormalities (anxiety, depression, psychosis). Kayser-Fleischer rings are crescents of green-brown discoloration of the cornea due to copper deposits in Descemet membrane; these are essentially always present in patients with neurologic involvement but may not be visible without a slit lamp. Hallervorden-Spatz syndrome, or neurodegeneration with brain iron accumulation type-1, is a rare, autosomal recessive disorder associated with macroscopic rust-brown discoloration of the globus pallidus and substantia nigra due to iron deposition. The clinical phenotype is variable but usually includes rigidity, involuntary movements, ataxia, and dystonia.