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Right leg supports

Steppage gait

Steppage gait

Ataxic gait

Ataxic gait

Spastic gait

(spastic paraparesis)

Gait cycle iff p

Posture and gait in youth (left) and old age (right)

Hypokinetic-rigid gait

(left, Parkinson disease; right, start delay/gait apraxia)

Right leg advances

Knee instability

(quadriceps paresis, leg dorsally angulated)

Spastic gait

(right hemiparesis)

Psychogenic gait disturbances

(histrionic movements)

Tremor, the most common movement disturbance, is an involuntary, rhythmic, oscillating movement of nearly constant amplitude. It can occur wherever movement is subserved by antagonistic muscle pairs. Different types of tremor may be classified by the circumstances in which they are activated or inhibited and by their location, frequency, and amplitude (Table 3, p. 357). Tremor amplitude is the most important determinant of disability. Parkinsonian tremor and essential tremor are the most common types. Rest tremor occurs in the absence of voluntary movement and is aggravated by emotional stress (excitement, time pressure) and mental activity (e. g., conversing, reading a newspaper). The

_ tremor subsides when the limbs are moved, but c

.O begins again when they return to the resting u position. Rest tremor is a typical feature of § parkinsonism.

^ Action tremors occur during voluntary move-,2 ment. Postural tremor occurs during main-5 tenance of a posture, especially when the arms are held outstretched, and disappears when the limbs are relaxed and supported. Essential tremor is a type of postural tremor. Kinetic tremor occurs during active voluntary movement; it may be worst at the beginning (initial tremor), in the middle (transitory tremor), or at the end of movement (terminal tremor). Intention tremor, the type that is worst as the movement nears its goal, is characteristic of cerebellar and brain stem lesions. Writing tremor and vocal tremor are examples of task-specific tremors. Dystonia-related tremors (e. g., in spasmodic torticollis or writer's cramp) can be suppressed by a firm grip (antagonistic maneuvers). Frequency. The frequency of tremor in each individual case is relatively invariant and may be measured with a stopwatch or by electromyo-graphy. Different types of tremor have characteristic frequencies, listed in the table below, but there is a good deal of overlap, so that differential diagnosis cannot be based on frequency alone.

2.5-5 Hz Cerebellar tremor, Holmes tremor 3-6 Hz Parkinsonian tremor 7-9 Hz Essential tremor, postural tremor in parkinsonism

62 7-12 Hz Physiological tremor, exaggerated physiological tremor 12-18 Hz Orthostatic tremor

Tremor genesis. The tremor of Parkinson disease is due to rhythmic neuronal discharges in the basal ganglia (internal segment of globus pal-lidus, subthalamic nucleus) and thalamus (ven-trolateral nucleus), which are the ultimate result of degeneration of the dopaminergic cells of the substantia nigra that project to the striatum (p. 210). Essential tremor is thought to be due to excessive oscillation in olivocerebellar circuits, which then reaches the motor cortex by way of a thalamic relay. Intention tremor is caused by lesions of the cerebellar nuclei (dentate, globose, and emboliform nuclei) or their projection fibers to the contralateral thalamus (ven-trolateral nucleus, p. 54). In any variety of tremor, the abnormal oscillations are relayed from the motor cortex through the corticospinal tracts (p. 44) to the spinal anterior horn cells to produce the characteristic pattern of alternating contraction of agonist and antagonist muscles.

Dangling arm

Rest tremor

Rest Tremor

*Due to coffee, tea, alcohol, medications (stimulants, neuroleptics, antidepressants, anticonvulsants, cyclosporine A), neurotoxins (heavy metals, insecticides, herbicides, solvents)

"Dystonia" is a general term for involuntary movement disorders involving sustained muscle contraction according to a stereotypic pattern, usually resulting in spasmodic or torsional movement and abnormal posture. Dystonic movements are usually exacerbated by voluntary activity. They may arise only during skilled activities such as writing or playing a musical instrument (action dystonia). Incomplete relief can be obtained by the avoidance of triggering activities and by the use of antagonistic maneuvers (e. g., placing the fingers on the chin, forehead or neck, or yawning, to counteract cervical dystonia). Dystonia may be classified by its distribution as focal (affects only one region of the body), segmental (two ad-.O jacent regions), multifocal (two or more nonad-u jacent regions), generalized, or lateralized § (hemidystonia), and by its etiology as either pri-^ mary (idiopathic) or secondary (symptomatic). ,2 Secondary dystonia is usually caused by a dis-5 order of copper, lipid, or amino acid metabolism, or by a mitochondrial disorder (p. 306 ff).

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