Sensory, Motor, and Reflex Examination




Key words

Sensory, Motor and Reflex Examination, neurologic examination

 




Introduction


The neurologic examination is an integral component of any musculoskeletal assessment. Determining the relative integrity of the neurologic system is an important step toward arriving at a proper diagnosis and ultimately appropriate management. Neurologic and musculoskeletal injuries can often mimic each other, and the symptoms from the patient’s history are not always reliable and specific. Objective findings from appropriately performed sensory, motor, and reflex testing can provide clarity for differentiating these categories of conditions. When a neurologic deficit is present, integration of the results of the different techniques of sensory, motor, and reflex testing should be used to localize the lesion to the extent possible. Additional diagnostic testing should be considered when further clarification of the clinical examination is needed.




Sensory Examination


The sensory examination is often the most challenging and time-consuming portion of the neurologic evaluation. When assessing a sensory disturbance, the examination should always be performed in the context of a detailed history, including the nature, distribution, and pattern of onset. Sensory complaints can be characterized by positive or negative symptoms. Examples of positive symptoms include spontaneous sensations such has tingling or shocking. Paresthesias are examples of positive symptoms and are described as tingling or pins and needles occurring spontaneously. Symptoms like this arising from nonnoxious stimuli are termed allodynia. Examples of negative symptoms include the lack of normal cutaneous sensation in a certain distribution or inability to identify the location of a body area in space. Numb, dead, woody, or leathery are terms used by patients to report negative symptoms.


The role of formal sensory testing is to establish objective evidence of the function of the sensory system. Subjective reports of sensory disturbance have less specificity and frequently less accuracy for establishing and localizing a sensory deficit. By contrast, diagnostic certainty is substantially improved by establishing sensory deficit in a specific distribution. It is also clinically useful to determine if the distribution of complaint is the same as the actual sensory deficit. With this in mind, the examiner should make every effort to be consistent in examination technique and to demonstrate reproducibility in the findings. All sensory testing requires cooperation from the patient; however, it should be performed in a manner that minimizes subjectivity from both the patient and the examiner. Actions to improve reliability include confirming the patient understands the test, shielding the examination from the patient’s line of site, and repeating the testing. Using tools such as Semmes-Weinstein monofilaments can add objectivity to the evaluation when needed.


Sensory testing is not considered highly sensitive for a neurologic deficit. It has been postulated that at least 50% of the sensory fibers of a peripheral nerve must be dysfunctional before a consistent clinical deficit is detectable. The sensory studies should always be used within the context of the motor and reflex examination as well. The extent of the sensory testing employed should usually be based on the context of the other examination findings.


Sensory deficits can occur as a result of CNS or peripheral nerve system injuries. Light touch and pin prick assessments are the most commonly used tests. Two-point discrimination can be valuable for assessment of both central and peripheral nerve lesions. Techniques to assess multiple sensory pathways are more frequently used in CNS lesions and include light touch, pressure, pain, temperature, vibration, and proprioception. A detailed knowledge of the sensory pathways is needed to reliably localize a lesion to the peripheral versus CNS insults. A detailed discussion of this anatomy is beyond the scope of this chapter. Peripheral nerve lesions should be differentiated between root level, plexus, main nerve trunk, or distal branch level. Knowledge of the dermatome patterns and peripheral nerve cutaneous patterns can help distinguish these potential lesion sites ( Fig. 2.1 ; ). The distribution of sensory disturbance can help localize the source of the insult. Sensory loss in the pattern of a dermatome suggests a radicular lesion, whereas a mononeuropathy will have a deficit limited to a peripheral nerve main trunk or one of its branches. When the pattern extends beyond a single nerve but remains in peripheral nerve patterns, a plexopathy or polyneuropathy is considered. Generalized, length-dependent neuropathies often produce a “stocking-glove” pattern. In this condition, the distal zone of maximum deficit gradually merges with a zone of less diminished sensation, and then into a region of normal sensation. When a generalized neuropathy is present, the examiner should be vigilant for focal neuropathies superimposed on a more generalized neuropathy. Identifying superimposed lesions requires appropriate history taking and often detailed side-to-side comparisons.




Figure 2.1


Illustration of the dermatome map.


Spinal cord pathology should be considered when a sensory impairment is seen in a distribution below a specific dermatomal level. Loss of sensation of the upper limbs and/or upper portion of the truncal area with sparing of the lower limbs or sacral sparing should raise the suspicion of an expanding intraspinal mass. The converse of this, with predominantly lower limb sensory loss, can be seen in the presence of a syrinx. Sensory disturbance on an entire side of the body suggests a central nervous system (CNS) lesion. Concomitant sensory loss on the same side of the face localizes the lesion to above the level of the pons. Sensory examination findings that do not follow physiologic boundaries can be suggestive of nonorganic etiology. Facial sensory disturbances that cross midline, as in a perioral pattern, can be associated with anxiety.


Distinguishing whether the sensory loss is across all modalities or selective can be useful to help determine the source of the deficit. For example, temperature and pain sensation are transmitted along small-diameter nerve fibers and then to the spinothalamic tract. Vibration perception is transmitted via large-diameter, heavily myelinated nerve fibers and then to the dorsal column–medial lemniscus tracts. Selective loss of sensation in these modalities can aid in localization of the lesion and in understanding its mechanism.


Sensory function can be divided clinically into primary and secondary (aka cortical) modalities. Primary modalities include light touch, pressure, pain, temperature, proprioception, and vibration sense. Cortical modalities require the synthesis and integration of the input from the primary modalities. This includes modalities such as two-point discrimination, stereognosis, and graphesthesia. Damage at the level of the parietal lobe can cause impairment of the secondary modalities when the primary modalities are intact. The best screening tests for sensory abnormality in a typical musculoskeletal examination are pain and light touch. The screening for pain sensory function is the use of a safety pin to lightly prick the regions of concern ( Fig. 2.2 ). The patient is asked whether the pinprick feels sharp in the affected area and typically in the same location of the opposite limb. While the examiner uses both the sharp and dull portion of the safety pin, the patient, with eyes closed, is asked to report whether the sensation is sharp or dull. A cotton wisp can be used to test light touch. The patient, with eyes closed, is asked to report when the cotton is felt ( Fig. 2.3 ).




Figure 2.2


Demonstration of the use of a safety pin to assess pain sensation.



Figure 2.3


Demonstration of the use of a cotton wisp to assess light touch.


Cortical sensory function can be evaluated with two-point discrimination, stereognosis, and graphesthesia. Two-point discrimination is performed by using two points, such as the tips of an unfolded paper clip to touch two closely separated locations on the skin. The patient’s eyes should be closed, and he or she asked ask if he or she can feel one or two points ( Fig. 2.4 ). Stereognosis testing is performed by asking the patient to identify a familiar object, such as a key or coin placed in the palm of the hand. Graphesthesia testing is performed by asking the patient to identify numbers that are written on the palm. Temperature sense can be tested with a cold tuning fork or with test tubes containing warm and cold water. When cold sensation is being tested, the body part must be normally warm.




Figure 2.4


Demonstration of the use of calipers to assess two-point discrimination.


Joint position sense is tested by moving the terminal phalanx of a patient’s finger or toe up or down a few degrees. If the patient cannot identify these tiny movements with eyes closed, similar testing should be performed on the larger joints such as the metacarpal phalangeal joint or wrist. The body part being tested should be grasped on the sides rather than the dorsal or ventral aspect to prevent the patient from using pressure cues to detect movement.


To test vibration sense, the examiner places a finger under the patient’s distal interphalangeal joint and presses a lightly tapped 128-cycle tuning fork on top of the joint. The patient detects the vibration and then notes its extinction about the same time as the examiner, who feels it through the patient’s digit. The age and size of the patient should be considered when assessing abnormalities of vibration sense. Devices designed to improve quantitative measurement of vibration sensation can also be used.


Provocative Maneuvers


Provocative maneuvers for eliciting sensory symptoms are notoriously nonspecific for reliably distinguishing true neurologic deficit, but they can sometimes provide clinical clues to the source of pain complaints. An example of this is a patient with chronic pain such as fibromyalgia, whose complaints of paresthesias are magnified by muscle palpation. Tender or “trigger” points in muscle can lead to reporting sensations described as paresthesias but are not related to an identifiable neurologic deficit.


Other maneuvers can potentially lead to dynamic nerve compression and provide clinical clues that contribute to localization of the source of a pain generator, but they are not specific for either neurologic deficit or nerve entrapment. Examples include the Spurling test in cervical radiculopathy, Adson test in thoracic outlet entrapment, and Phalen sign in median nerve entrapment at the carpal tunnel. Techniques of this nature can potentially produce neurologic or neurologic-like symptoms, but they cannot be expected to alter the sensory examination.


Tapping over a suspected focal peripheral neuropathy to reproduce neuritic symptoms and assess for sensitivity is a frequently cited technique and has been termed the Tinel sign. Tinel originally described this technique as a method to determine the location of recovery of regenerating axons after trauma. In his description, the presence of the sign at the location that was being tapped was indicative that the nerve had regenerated to that position. Localized sensitivity can develop over an area of peripheral nerve injury; however, percussion over a normal peripheral nerve in a superficial location will also induce pain and paresthesias. The use of this technique should not be considered reliable confirmation of a focal entrapment neuropathy.




Motor Examination


The role of motor testing is to assess the patient’s strength. Reports of weakness are not always due to a true motor deficit. Some complain of weakness when they are actually referring to fatigue, malaise, or incoordination. Strength testing is not the same as power, which refers to the rate of performing work. Manual muscle testing is the most commonly used technique for testing strength. With manual muscle testing, the strength of specific muscle groups is tested against resistance, and one side of the body is compared with the other. It is performed by providing a counterforce on a specific point on the limb against the patient’s best effort ( Fig. 2.5 ; ).




Figure 2.5


Demonstration of the technique of manual muscle testing.


There are a variety of different classification systems for grading manual muscle testing. Most are based on the Medical Research Council 0–5 scale ( Table 2.1 ).



Table 2.1

Medical Research Council 0–5 Scale







































Objective Grade Qualitative Description Observation Range of Motion
5 Normal Antigravity plus full resistance Full range of motion
4 Diminished Antigravity plus some resistance Full range of motion
3 At least antigravity Antigravity only Full range of motion
2 Poor Gravity omitted Full range of motion
1 Trace Evidence of activation Partial range of motion
0 No activation No evidence of activation n/a

n/a, not applicable.


There have been significant modifications of this format by many authors. Most of these scales give ordinal data. This means the values are on an arbitrary numerical scale where the exact numerical quantity has no significance beyond its ability to establish a ranking over the other values. Some of the modifications have been created to provide a designation between these ordinal measures.


In the Medical Research Council scale, the grades of 0, 1, and 2 are tested in a position that minimizes the effect of gravity. This is performed while having the patient’s contraction perpendicular to gravitational force. Grades of 3, 4, and 5 are tested with the contraction against gravity. One difficulty with the higher grades in this system is that gravity has more impact on heavier limbs or body regions compared with smaller areas. An example is testing hip flexion in a supine position in comparison with toe extension. Detecting subtle weakness in strong muscles with relatively short lever arms such as the gastroc-soleus complex can also be challenging with manual testing.


Another difficulty with the comparison of higher grades between different examiners is the relative subjectivity of the assessment. Distinguishing mild weakness can be dependent on multiple factors. This includes the size, age, fitness level, and general health of the patient. It also can be potentially affected by those same factors in the examiner. Other factors can complicate the assessment including orthopedic conditions that preclude full range of motion and other sources of pain or psychological factors that might limit full effort.


Some authors have presented other manual muscle testing protocols in an effort to minimize some of these limitations. Daniels and Worthingham proposed a more functional grading system by testing motion that uses all of the agonists and synergists involved in a particular motion. Kendall and McCreary proposed testing a specific muscle rather than a motion for strength. This method requires a considerably higher skill level with detailed knowledge of anatomy and kinesiology. Regardless of the method used, challenges of subjectivity and variability of patient effort remain.


It is best to use a grading system for motor testing that will be understood by other practitioners who might also be caring for the patient. It is therefore preferable to use a highly reproducible, easily performed examination. A consistent method of performing the examination is necessary for reproducible results.


The testing should be explained to the patient in simple terms to invoke optimum cooperation. In the presence of asymmetric weakness, the testing should first be performed on the uninvolved or less involved side. This helps to properly gauge the contralateral strength and establish that the patient understands the directions for the involved side.


The limbs being examined should first be assessed for passive motion limitations such as joint deformity or joint or muscle contracture. Any orthopedic limitation affecting normal motion should be noted and accounted for when considering strength.


Each muscle group or limb motion should be tested in a consistent fashion. Differences in the point of application of the resistive force will result in varying assessments of strength. Shorter lever arms provide higher strength against the same resistance as longer lever arms. The application of resistance should be as distal as possible from the axis of movement on the moving segment without crossing another joint. The patient should be positioned comfortably on a firm surface with the limb in the correct testing position. The correct testing position ensures that the muscle fibers are correctly aligned. Resistance is applied in a direction opposite the muscle’s rotary component and at right angles to the line of the pull of the muscle fibers. The resistance should be applied gradually to give the patient sufficient time to provide resistance. The proximal segment that uses counterpressure to the examiner’s resistance should be stabilized to avoid unnecessary movement or muscle substitution. It can be beneficial to place some stronger muscles in a position of mechanical disadvantage when investigating subtle weakness. For example, when assessing strength of the triceps brachii, place the elbow in 90 degrees of flexion instead of full extension, thus limiting the resistance of the extended joint.


When the patient demonstrates that he or she can move the area of interest through full range of motion against gravity, then resistance is applied. If the patient is unable to oppose gravity, then the test movement is positioned in a direction, usually in the transverse plane, to minimize the influence of gravity. Some recommend that the test be repeated up to three times for consistency to determine the muscle strength grade. Manual muscle testing for weakness should include not only muscles in a pattern of the various myotomes, but consideration should also be given to the pattern of peripheral nerves and their branches when appropriate.


Other Measurement Tools


Motor testing can be better quantified by use of various measurement tools. A method of strength testing using dedicated measuring devices such as dynameters, strain gauges, and other apparatus is called dynamometry. There are tools available that provide both isometric and isokinetic assessments. Isometric testing provides information about force production with a specific, fixed joint angle. Isokinetic testing measures torque across a joint as it moves through its range of motion.


Advantages of testing with these tools include providing interval data with a continuous scale of grades in contrast to the more limited ordinal scale used with conventional manual muscle testing. For this reason, quantitative motor testing with dynamometry typically provides better information for subtle changes in strength that would not be reliably reflected in manual muscle tests. Dynamometry is also useful for greater reproducibility in clinical trials. Disadvantages of motor assessment with dynamometry include a relative limitation of muscle groups that can be reliably tested. Follow-up testing by another clinician would require that the clinician also have the same tools available. Additionally, some of the tools for testing, particularly for isokinetic assessment, can be relatively expensive.


Functional Measures


Functional assessments are also an important component of motor testing both as a screening test and for identifying deficiencies that might not be evident with routine motor testing. Isolation of specific muscles is often challenging because they generally work in conjunction with synergistic and antagonist muscles. Additionally, the components of the motor cortex represent movements rather than contractions of individual muscles. Assessments of gait or active shoulder motion are examples of complex motor evaluations that can serve as a screen for underlying weakness. Tests such as single leg squats or toe raises can demonstrate side-to-side asymmetry in strength that might not be evident with routine manual muscle testing.

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Jul 23, 2019 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Sensory, Motor, and Reflex Examination
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