Overview of the Motor Examination

Weakness is a common abnormality and can follow many
patterns. Terminology may become problematic. For instance, weakness
may be generalized or localized, symmetric or asymmetric, proximal or
distal, or upper motor neuron or lower motor neuron. The term focal is
often used to imply asymmetry; a patient with a hemiparesis is said to
have a focal examination. The term generalized is often used to imply
symmetry, even though the weakness may not truly be generalized. A
disease may cause weakness in a particular distribution that is
bilaterally symmetric (e.g., the scapuloperoneal syndromes), but these
are not generally regarded as focal even though the involvement is very
localized. A patient with bilateral carpal tunnel syndrome or bilateral
peroneal nerve palsies would most properly be described as having a
multifocal pattern of weakness, even though the weakness is bilateral
and symmetric. The term nonfocal is often used to describe a patient’s
neurologic examination, particularly by non-neurologists. The
implication is usually that the examination is normal, or at least that
there is no asymmetry. It is a poor and not very helpful term. A
patient with Guillain-Barré syndrome causing generalized weakness and
impending respiratory failure would have a nonfocal examination, yet be
critically ill.

Muscle tone may be increased (hypertonia) or decreased
(hypotonia). Hypertonia comes in two common variants: rigidity and
spasticity. When the increased tone occurs to more or less the same
degree throughout the range of passive motion of a limb, and is
independent of the speed of the movement, it is referred to as
rigidity. When the hypertonia is most marked near the middle of the
range of motion and is more apparent with fast than with slow passive
movement, it is referred to as spasticity. One of the key
characteristics of spasticity is that the hypertonus is velocity
dependent, most evident with rapid movements. In lead pipe (plastic)
rigidity, there is smooth resistance throughout the range independent
of the rate of movement. Gegenhalten (paratonia) is an increase in tone
in a limb more or less proportional to the examiner’s attempt to move
it. In cogwheel rigidity there is ratchety, jerky, tremulous variation
in the hypertonia, due primarily to superimposed tremor. Spastic
hypertonia is typically associated with increased deep tendon reflexes,
loss of superficial reflexes, and Babinski signs. Cogwheel rigidity
occurs in Parkinson disease and related conditions. Gegenhalten is
usually associated with other abnormal neurologic signs depending on
the etiology. The term dystonia refers to transient or sustained
hypertonic conditions that do not fit into the other categories.
Hypotonia occurs in two primary settings in the adult: myopathies and
cerebellar disease. Infantile hypotonia (floppy baby) is a common
clinical problem. The differential diagnosis of infantile hypotonia is
extensive, and the workup of a floppy baby is a frequent exercise in
pediatric neurology.

Muscle mass or volume may be decreased (atrophy) or
increased (hypertrophy). Neurogenic atrophy results from a lesion
involving the anterior horn cells, nerve root, or peripheral nerve
innervating a muscle; it may be severe. Muscle diseases usually cause
only mild to moderate atrophy of the involved muscles. Disuse atrophy
occurs after immobilization, as when a limb is in a cast, and is
usually mild to moderate in severity and recovers quickly with
resumption of use.

True muscle hypertrophy results from an increase in the
size of the muscle. It is most often physiologic hypertrophy from heavy
use, but it can occur in certain neuromuscular disorders.
Pseudohypertrophy refers to apparent muscle enlargement due to
replacement of diseased muscle by fat and fibrous tissue. Enlarged calf
muscles in patients with Duchenne muscular dystrophy are a classic
example of muscle pseudohypertrophy.

Abnormal involuntary movements occur in a host of
neurologic conditions. They come in many forms, ranging from tremor to
chorea to muscle fasciculations to myoclonic jerks. The only common
characteristic is that the movements are spontaneous and not under
volitional control. Involuntary movements may be rhythmic or random,
fleeting or sustained, predictable or unpredictable. They may occur in
isolation or be accompanied by other neurologic signs. Common types
include tremor, chorea, athetosis, hemiballismus, dystonia, tics, and
dyskinesias.

Coordination and control of fine motor movements are
delicate functions that require smooth interactions between the
different components of the motor system as well as normal sensory
function. The cerebellum is a critical component, and disease of the
cerebellum frequently causes impaired coordination in the absence of
weakness or other motor abnormalities. But poor coordination may also
be a manifestation of corticospinal tract or extrapyramidal disorders.