SENSORY EXAM: NORMAL EXAM
Light touch (thigmesthesia) is used as a screening test for touch. Both the spinothalamic and DCML systems serve this sensation so it is not specific for either one. A cotton tip applicator or fine hair brush is used. Select areas from different dermatomes and peripheral nerves and compare right versus left.
Pain – Upper Extremities
Pain is one of the principle sensory modalities of the spinothalamic system. The sharp end of a broken wooden cotton tip applicator can be used then discarded. It is important for the patient to be able to identify the sensation as sharp and then compare between dermatomes, distal versus proximal and right versus left for the upper extremities.
Pain – Lower Extremities
Pain is one of the principle sensory modalities of the spinothalamic system. The sharp end of a broken wooden cotton tip applicator can be used then discarded. It is important for the patient to be able to identify the sensation as sharp and then compare between dermatomes, distal versus proximal and right versus left for the lower extremities.
Temperature is the other sensory modality that is used to test the spinothalamic system. Tubes or vials of hot and cold water can be used but this is usually impractical. Using a tuning fork, which is normally perceived as cool or cold to the touch, compare between dermatomes and right versus left.
Vibratory sensation (pallesthesia) is one of the sensory modalities of the DCML system. It is tested by using a 128 Hz tuning fork and placing the vibrating instrument over a bone or boney prominence. By varying the force of vibration and comparing the patient to yourself you can detect any deficits. Compare distal versus proximal and right versus left.
Position sense (proprioception), another DCML sensory modality, is tested by holding the most distal joint of a digit by its sides and moving it slightly up or down. First, demonstrate the test with the patient watching so they understand what is wanted then perform the test with their eyes closed. The patient should be able to detect 1 degree of movement of a finger and 2-3 degrees of movement of a toe. If the patient can't accurately detect the distal movement then progressively test a more proximal joint until they can identify the movement correctly.
Tactile movement as well as the remaining sensory tests are discriminatory sensory tests that examine cortical somatosensory (parietal lobe) function and require an intact DCML system. Tactile movement tests the patient's ability to detect the direction of a 2-3 cm cutaneous stimulus.
Two-point discrimination is tested by using calipers or a fashioned paper clip. The smallest and most dense sensory units are located in those areas that have the greatest somatosensory cortical representation. The patient should be able to recognize two-point separation of 2-4 mm on the lips and finger pads, 8-15 mm on the palms and 3-4 cm on the shins.
Graphesthesia is the ability of the patient to identify characters that are written on the skin using a dull pointed object. The examiner demonstrates the test by writing single numbers on the palm of the hand while the patient is watching. The patient then closes their eyes and identifies numbers that are written by the examiner.
Stereognosis is the ability to identify objects that are placed in the hand when the eyes are closed. The patient is given common objects and asked to identify them without looking at them. The inability to do this called astereognosis and indicates parietal lobe dysfunction.
Double Simultaneous Stimulation
The patient should be able to attend to and identify a tactile stimulus that is applied to both sides of the body at the same time. Double simultaneous stimulation (DSS) is tested by touching homologous parts of the body on one side, the other side or both sides at once with the patient identifying which side or if both sides are touched with their eyes closed. If the patient neglects one side on DSS (extinction or simultanagnosia) this indicates dysfunction of the contralateral posterior parietal lobe.
The Romberg test is a test of proprioception. This test is performed by asking the patient to stand, feet together with eyes open, then with eyes closed. The patient with significant proprioceptive loss will be able to stand still with eyes open because vision will compensate for the loss of position sense but will sway or fall with their eyes closed because they are unable to keep their balance.