If proprioception is abnormal in axial structures, the patient will be unable to maintain his balance with feet together and eyes closed (Romberg sign). This test is often interpreted imprecisely. In the Romberg position, even a normal person whose eyes are closed will sway slightly, and the patient who lacks balance because of cerebellar ataxia or some other motor disorder will sway considerably more if his visual cues are removed. Only a marked discrepancy in balance with eyes open and with eyes closed qualifies as a Romberg sign. The most certain indication of abnormality is the need to step to the side or backward to avoid falling. Mild degrees of unsteadiness in an anxious or suggestible patient may be overcome by diverting his attention, for example, by having him touch the index finger of each hand alternately to his nose while standing with eyes closed or by following the examiner’s finger with his eyes. Patients with authentic proprioceptive problems will sway when there gaze is diverted from the ground and then become more unsteady when the eyes are closed. Patients with factitious unsteadiness usually will remain stable when they follow the examiner’s fingers or look alternately at the ceiling and then at a distant object but then appear to be very unsteady when the eyes are closed. It is important to remember that any defect in proprioception (e.g., peripheral neuropathy, myelopathy or vestibulopathy) will lead to a Romberg sign even though the sign, described by Moritz Romberg, was meant to diagnose tabes dorsalis.
Abnormalities of position sense may also be disclosed when the patient has his arms outstretched and eyes closed. The affected arm will wander from its original position; if the patient’s fingers are spread apart, they may undergo a series of changing postures (“piano-playing” movements, or pseudoathetosis); in attempting to touch the tip of his nose with the index finger, the patient may miss the target repeatedly, but the performance is corrected when the eyes are open.
Testing of Vibratory Sense
This is a composite sensation comprising touch and rapid alterations of deep-pressure sense but for clinical work, it may be considered a useful single modality. The cutaneous structure capable of registering stimuli of frequencies that are used for clinical testing is probably the pacinian corpuscle. The conduction of vibratory sense depends on large sensory fibers that ascend mainly in the dorsal columns of the cord. Consequently, it is rarely affected by lesions of single nerves but will be disturbed in patients with disease of multiple peripheral nerves, dorsal columns, medial lemniscus, and thalamus. Vibration and position sense are usually impaired in similar conditions, although one of them (most often vibration sense) may be affected disproportionately. With advancing age, vibration is the sensation most commonly diminished, especially at the toes and ankles (see further on).