Syndrome of cerebellar ataxia, neuropathy and vestibular areflexia: diagnosis by caloric vestibular stimulation.

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) is a recently-described progressive degenerative disease whose exact prevalence remains unknown. This syndrome appears mainly sporadically and occasionally affects siblings. This has led researchers to consider the possibility of a recessive inheritance pattern, but the disease has not yet been linked to changes at a specific locus. According to published cases, age at onset ranges from 33 to 71 years; after 10 years with the disease, most patients require support when walking. We present the case of a 74-year-old man who for 21 years had experienced gait instability exacerbated by darkness, and diminished foot sensation, which progressively increased until he became unable to walk unaided 5 years ago. Neurological examination revealed absent Achilles reflexes, wide-based stance, positive results on the Romberg test, and markedly ataxic gait requiring bilateral support. Vibratory sensation was abolished below the iliac crests, diminished above that level, and normal in the face; algesia was preserved. The patient presented dysmetria, movement decomposition with essential tremor, scanning dysarthria, saccadic movements during eye tracking, horizontal and vertical gaze-evoked nystagmus, and refixation saccade in the horizontal plane during the Halmagyi head thrust manoeuvre. Among complementary data, videonystagmography (VNG) showed horizontal spontaneous pendulum movements in the primary gaze position and eye tracking consisting of saccadic movements. Bilateral caloric stimulation induced only small erratic eye movements and the audiometry test showed normal hearing. The brain MRI revealed cerebellar global atrophy, especially in the superior part of the vermis, with crus I impairment; the membranous labyrinths showed no changes. MR imaging showed normal spinal cord morphology, size, and signal. An electroneurography study revealed absence of sensory nerve action potentials, as well as normal motor conduction velocity and normal motor unit action potential amplitudes in the nerves in all 4 limbs. Dynamic mutations of spinocerebellar ataxia (SCA) types 1, 2, 3, 6, and 7, Friedreich ataxia (FRDA), and fragile