Muscle volume and contour. The volume and contour of the muscles give information about the presence of either atrophy or hypertrophy. Muscle atrophy, or amyotrophy, may be defined as the wasting or diminution in size of a muscle part. It is usually accompanied by changes in shape or contour. Its results from disorders affecting the anterior horn cell, the nerve root, the peripheral nerve, or the muscle itself. Muscle hypertrophy is an increase in the bulk, or volume, of muscle tissues. It may be the result of excessive use of the muscles, or it may occur on a pathologic basis. Muscle volume and contour are examined and atrophy or hypertrophy by inspection, palpation, and measurement. By means of inspection the general muscular development of the size of the muscles are noted, and special attention is paid to abnormalities in volume and contour and to evidence of atrophy and hypertrophy. Symmetric parts of the two sides of the body should be compared. The muscle masses should also be carefully palpated, and their volume, contour, and consistency noted. To determine the degree of atrophy or hypertrophy, measurements may be essential. The appraisal of muscle bulk and contour should be correlated with the other items of the motor examination, especially with the evaluations of strength and tone.
If muscular changes in the form of atrophy or hypertrophy are present, and if we need to refine the etiology of lesion a muscle biopsy should be considered. Electromyography aids in the differential diagnosis of muscular atrophy. It helps to decide the level of lower motor neuron and its peripheral axons lesion.
Motor strength and power. Motor strength and power indicate the capacity to exert and release force. It’s necessary to examine both the power of movement and the strength of contraction. In examining strength and power we are interested especially in voluntary, or active, motility. This is tested by having the patient carry out movements against the resistance of the examiner, and by having him resist active attempts on the part of the examiner to move fixed parts. Impairment of strength and power results in weakness, or paresis, absence of strength. Associated functions and abnormalities must be also noted. Abnormal fatigability may precede other objective manifestations of some neuromuscular disorders (such as myasthenia). There is a marked individual variation in muscle strength.
The paralysis may involve one muscle, a group of muscles, certain movements, or one or more extremities. A monoplegia is the paralysis of one extremity; diplegia- is the paralysis of extremities on the two sides of the body; hemiplegia, of one half of the body; paraplegia, the legs or the lower parts of the body; quadriplegia (tetraplegia) – the paralysis of all extremities. Hemiplegia alternans affects the upper extremity on one side of the body and the lower extremity on the other side.
When a muscle is maintained in a position of contraction or shortening for a period of time, a contracture may develop: the muscle cannot be stretched to normal limits without considerable pressure and the production of pain. Contractures may develop following prolonged spasm of muscles, in association with spastic paralysis.
To test motor power, the various movements at each joint and the strength of each important muscle should be examined individually. He is instructed to either resist active attempts by the examiner to move fixed parts or to initiate and carry out movements that are resisted by the examiner. Corresponding muscles on the two sides of the body should always be compared. Both active and passive movements should be tested and if limitation of movement is accompanied by discomfort or pain, this should be noted. In the presence of coma assessment of motor function may have to depend upon the presence of spontaneous movements, the position of the extremities, asymmetries of voluntary movements on the two sides, or withdrawal of an extremity in response to painful stimulation. Hemiplegia may be diagnosed if the contraction of the facial muscles on one side is absent and the similar extension and external rotation of the thigh and leg is present. It is usually possible to evaluate muscle strength and power sufficiently well without recourse to special instruments (e.g. dynamometer). Muscle function may be graded in various ways, but the following is an acceptable classification:
0. No muscular contraction occurs;
1. Aflicker, or trace, of contraction occurs without actual movement, or contraction may be palpated in the absence of apparent movement; there is minimal or no motion of joints (0% - 10% of normal movement);
2. The muscle moves the part through a partial arc of movement with gravity eliminated (11% - 25% of normal movement);
3. The muscle completes the whole arc of movement against gravity (26% - 50% of normal movement);
4. The muscle completes the whole arc of movement against gravity together with
variable amounts of resistance (51% - 75% of normal movement);
5. The muscle completes the whole arc of movement against gravity and maximum amounts of resistance several times without signs of fatigue. This is normal muscular power (76% - 100% of normal movement).
Examination of muscle tone. Tone, or tonus, has been defined as the tension of the muscles when they are relaxed, or as their resistance to passive movement when voluntary control is absent. In testing tone, the examiner should attempt to secure the complete cooperation of the patient, who should be comfortable and relaxed. Palpation of the muscles reveales their consistency, passive elasticity, firmness, or turgor. The most important criterion in the examination of tone is the resistance of muscles to passive manipulation when they are relaxed and when voluntary control is absent. Loss or diminution of tone is classified as hypotonicity, and pathologic increase, as hypertonicity. Hypotonicity or flaccidity results from involvement of the spinomuscular level or interference with the proprioceptive pathways, but may also be present with cerebellar lesions. It is characterized by a decrease or loss of normal tone. The muscle is flaccid and flabby, or soft to palpation. The excursion at the joint may be normal, but is usually increased. The decrease in tone appears in the anterior horn cell damage, abnormalities of the muscle itself or of the myoneural junction.
Hypertonicity is usually caused by lesions central to the anterior horn cells, or by interruption of impulses from supraspinal regions. It is seen most frequently with dysfunction of the so-called extrapyramidal and corticospinal levels, and is caused by either interruption of impulses that normally inhibit lower centers or imbalance of facilitatory and inhibitory centers, with consequent alteration of the ?- and ?-motor neuron balance or lowering of the threshold of the spinal reflexes.
Spasticity. This occurs in association with lesions of the pyramidal or corticospinal level of function. There may be an elastic, springlike resistance to stretching at the beginning of movement, especially if the part is moved abruptly or suddenly, following which the muscle resists to a certain point and then suddenly relaxes – the phenomenon sometimes referred to as the clasp-knife type of resistance.
Extrapyramidal rigidity occurs with lesions of the basal ganglia or of some other portion of the extrapyramidal level of motor function or its connections with the brain stem reticular formations. This phenomenon is called “cogged-wheel symptom”. Tonus is expressed in the same manner in the group of flexors and extensors.