NOSOLOGICAL ENTITIES? Cervical vertigo

Proprioceptive input from the neck participates in the coordination of eye, head, and body posture as well as spatial orientation. On this basis it has been argued that a syndrome of cervical vertigo might exist. However, cervical vertigo is a controversial clinical entity and patients with suspected disease often have alternative bases for their symptoms. The neck contains mechanisms directly involved in balance control (neck aVerents), cardiovascular control (carotid bodies), and purely vascular structures (carotid and vertebral arteries). Neck movements are also invariably associated with head movements. Thus, experiencing unsteadiness or vertigo associated with neck movements could be due to a disorder in vestibular, visual, vascular, neurovascular, or cervicoproprioceptive mechanisms. Table 1 summarises the possible diVerential diagnoses. Without further specification, however, the term cervical vertigo is reserved for cases where the suspected mechanism is proprioceptive. The reasoning is as follows. The perception of head rotation is mediated by vestibular, proprioceptive, or visual receptors. Vertigo should therefore be induced by stimulation of any of these systems. Degenerative or traumatic changes of the spine could induce distorted sensations of head motion (vertigo). This line of thought is, however, not as straightforward as it seems. Clearly, vestibular lesions or experimental vestibular activation (for example, a caloric test) produce powerful illusions of self motion. Similarly, visually induced illusion of self motion is readily experienced—for example, the feeling that the train we are in has started to move oV when, in fact, it is the train next to ours which has done so. Evoking a clear sensation of head turning by cervical stimulation is, by contrast, not so straight forward. To start with, to investigate neck proprioception, the head must be immobilised while the trunk is rotated. Unless this technical precaution is taken, any normal or abnormal sensations of head turning can always be due to vestibular stimulation. With this approach, under special conditions of perceptual uncertainty (for example, both the subject’s head and trunk can be independently rotated in the dark), trunk rotation can induce sensations of head turning. However, when the subject’s head is unambiguously fixed, or in normal viewing conditions, trunk rotation does not induce sensations of head turning. This is so, even in certain pathological conditions when trunk rotation is capable of inducing strong nystagmus—for example, bilateral absence of vestibular function, or occasionally, in cerebellar lesions. Questions relevant for the discussion of cervical vertigo are: What is the functional relevance of neck aVerent input and how does the lack of or distortion of such input lead to vertigo or disequilibrium? Ataxia and unsteadiness occurring with sensory polyneuropathy