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INTRODUCTION

  • Parkinson disease (PD) has highly characteristic neuropathologic findings and a clinical presentation, including motor deficits and, in some cases, mental deterioration.

PATHOPHYSIOLOGY

  • The true etiology of PD is unknown.

  • Two hallmark features in the substantia nigra pars compacta are loss of neurons and presence of Lewy bodies. The degree of nigrostriatal dopamine loss correlates positively with severity of motor symptoms.

  • Reduced activation of dopamine1 and dopamine2 receptors results in greater inhibition of the thalamus and reduced activation of the motor cortex. Clinical improvement may be tied to restoring activity more at the dopamine2 receptor than at the dopamine1 receptor.

CLINICAL PRESENTATION

  • PD develops insidiously and progresses slowly over many years.

General Features

  • The patient exhibits bradykinesia and at least one of the following: resting tremor, rigidity, or postural instability. Asymmetry of motor features is supportive.

Motor Symptoms

  • Only two-thirds of patients with PD have tremor on diagnosis, and some never develop this sign. Tremor in PD is present most commonly in the hands, sometimes with a characteristic pill-rolling motion.

  • The patient experiences hypokinetic movements, decreased manual dexterity, difficulty arising from a seated position, diminished arm swing during ambulation, dysarthria (slurred speech), dysphagia (difficulty with swallowing), festinating gait (tendency to pass from a slow to a quickened pace), flexed posture, “freezing” at initiation of movement, hypomimia (reduced facial animation), hypophonia (reduced voice volume), and micrographia.

Autonomic and Sensory Symptoms

  • The patient experiences bladder dysfunction, constipation, diaphoresis, fatigue, olfactory impairment, orthostatic intolerance, pain, paresthesia, paroxysmal vascular flushing, seborrhea, sexual dysfunction, and sialorrhea (drooling).

Mental Status Changes

  • The patient experiences anxiety, apathy, bradyphrenia (slowness of thought processes), cognitive impairment, depression, and hallucinosis/psychosis.

Sleep Disturbances

  • The patient experiences excessive daytime sleepiness, insomnia, obstructive sleep apnea, and rapid eye movement (REM) sleep behavior disorder.

DIAGNOSIS

  • The clinical diagnosis of PD is based on the presence of bradykinesia and at least one of the three other features: muscular rigidity, resting tremor, and postural instability (Table 57-1).

  • There are no laboratory tests available to diagnose PD, including genetic testing.

  • Neuroimaging may be useful for excluding other diagnoses.

  • Medication history should be obtained to rule out drug-induced parkinsonism.

TABLE 57-1Diagnostic Criteria and Differential Diagnosis for Parkinson Disease

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