Porth's Essentials of Pathophysiology, 4e

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Disorders of Neuromuscular Function

C h a p t e r 3 6

Assessment of Motor Function Disorders of the motor system produce signs and symp- toms that can be used in localizing the disorder. These include changes in muscle characteristics (strength, bulk, and tone), spinal reflex activity, and motor coor- dination. 6 The distinction between LMNs and UMNs is important because each class of neurons produces dis- tinctive symptoms. Muscle Strength, Bulk, andTone Muscle Strength. Abnormalities in any part of the motor pathway can produce impaired strength or mus- cle weakness. Paralysis refers to loss of movement, and paresis to weakness or incomplete loss of strength. The pattern of weakness may be helpful in the localization of the lesion. Monoparesis or monoplegia results from the destruction of pyramidal UMN innervation of one limb; hemiparesis or hemiplegia, both limbs on one side; diparesis or diplegia or paraparesis or paraplegia, both upper or lower limbs; and tetraparesis or tetraplegia, also called quadriparesis or quadriplegia, all four limbs (Fig. 36-4). Paresis or paralysis can be further designated as of UMN or LMN origin. UMN lesions of the motor cor- tex or corticospinal tract typically affect the flexors in the upper extremities more than the extensors, whereas in the lower extremities, the flexors are more affected. In LMN or peripheral nerve disorders, the weakness is predominantly in the distal limb, whereas in muscle disorders, such as muscular dystrophy, proximal limb function may be affected sooner than distal limb function. Muscle Bulk. The size of muscle (whether muscles are normal sized, enlarged, or atrophied) also helps local- ize the lesion, and sometimes provides helpful hints to the pathologic process. Muscular atrophy, or loss of muscle bulk, usually results from LMN lesions as well as diseases of the muscles themselves. Hypertrophy refers to an increase in muscle bulk with a propor- tionate increase in strength. Pseudohypertrophy, as occurs with Duchenne muscular dystrophy, refers to an increase in bulk without an accompanying increase in strength. Muscle Tone. Muscle tone is the normal state of muscle tension. It is assessed by palpating the muscle while at rest and during passive stretching. With the person at rest, the joints are put through the normal range of motion (flexion and extension) by the exam- iner. Disorders of skeletal muscle tone are characteris- tic of many nervous system lesions. Any interruption of the myotatic or stretch reflex circuitry by periph- eral nerve injury, pathologic process of the neuromus- cular junction, injury to the spinal cord, or damage to the corticospinal system can result in disturbances of muscle tone.

Monoplegia

Hemiplegia

Tetraplegia or quadriplegia

Paraplegia

Abnormalities of muscle tone may be described as hypotonia (less than normal), flaccidity (absent), or hypertonia, rigidity, spasticity, or tetany (all indicat- ing higher-than-normal tone). Typically, UMN lesions produce increased tone, whereas LMN lesions produce decreased tone. Increased resistance that varies and commonly becomes worse at the extremes of the range of motion is called spasticity. Resistance that becomes worse throughout the range and in both directions is referred to as lead-pipe rigidity. Decreased resistance suggests disease of the LMNs or the acute stages of spi- nal cord injury. Marked floppiness indicates hypotonic or flaccid muscles. Fasciculations. Fasciculations are visible squirming and twitching movements of muscle fibers that can be seen as flickers under the skin. 7 They are caused by spontaneous FIGURE 36-4. Areas of the body affected by monoplegia, hemiplegia, tetraplegia or quadriplegia, and paraplegia. The shaded area shows the extent of motor and sensory loss. (From Hickey JV. The Clinical Practice of Neurological and Neurosurgical Nursing. 3rd ed. Philadelphia, PA: J.B. Lippincott; 1997.)