Chapter 56: Parkinson Disease

INTRODUCTION

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

PATHOPHYSIOLOGY

• 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.

• Initial symptoms may be sensory, but as the disease progresses, one or more classic primary features present (eg, resting tremor, rigidity, bradykinesia, and postural instability that may lead to falls).

• Resting tremor is often the sole presenting complaint. However, only two thirds of PD patients have tremor on diagnosis, and some never develop this sign. Tremor is present most commonly in the hands, often begins unilaterally, and sometimes has a characteristic “pill-rolling” quality. Resting tremor is usually abolished by volitional movement and is absent during sleep.

• Muscular rigidity involves increased muscular resistance to passive range of motion and can be cogwheel in nature. It commonly affects both upper and lower extremities; neck and facial muscles may be affected.

• Intellectual deterioration is not inevitable, but some patients deteriorate in a manner indistinguishable from Alzheimer disease.

• Nonmotor symptoms are common and must be identified, treated, and monitored (Table 56–1).