Peripheral nerves are pathologically small in cerebellar ataxia neuropathy vestibular areflexia syndrome: a controlled ultrasound study

BACKGROUND AND PURPOSE

Sensory neuronopathy is a cardinal feature of cerebellar ataxia neuropathy vestibular areflexia syndrome (CANVAS). Having observed that two patients with CANVAS had small median and ulnar nerves on ultrasound, we set out to examine this finding systematically in a cohort of patients with CANVAS, and compare them with both healthy controls and a cohort of patients with axonal neuropathy. We have previously reported preliminary findings in seven of these patients with CANVAS and seven healthy controls.

METHODS

We compared the ultrasound cross-sectional area of median, ulnar, sural and tibial nerves of 14 patients with CANVAS with 14 healthy controls and 14 age- and gender-matched patients with acquired primarily axonal neuropathy. We also compared the individual nerve cross-sectional areas of patients with CANVAS and neuropathy with the reference values of our laboratory control population.

RESULTS

The nerve cross-sectional area of patients with CANVAS was smaller than that of both the healthy controls and the neuropathy controls, with highly significant differences at most sites (P < 0.001). Conversely, the nerve cross-sectional areas in the upper limb were larger in neuropathy controls than healthy controls (P < 0.05). On individual analysis, the ultrasound abnormality was sufficiently characteristic to be detected in all but one patient with CANVAS.

DISCUSSION

Small nerves in CANVAS probably reflect nerve thinning from loss of axons due to ganglion cell loss. This is distinct from the ultrasound findings in axonal neuropathy, in which nerve size was either normal or enlarged. Our findings indicate a diagnostic role for ultrasound in CANVAS sensory neuronopathy and in differentiating neuronopathy from neuropathy.

Treatment of severe axial tardive dystonia with clozapine: case report and hypothesis

We report a patient with severe axial tardive dystonia who has had dramatic improvement for 4 years after treatment with the atypical antipsychotic drug clozapine (625 mg/day). Clozapine differs from conventional neuroleptics in that it has higher affinity for D1 and lower affinity for D2 dopamine receptors than do conventional antipsychotics, which are relatively selective D2 antagonists. We propose that repetitive stimulation of the D1 receptor by endogenous dopamine, resulting in sensitization of the D1-mediated striatal output in the presence of D2 receptor blockade, is a fundamental mechanism mediating tardive dyskinesia, including the dystonic type. According to this hypothesis, it is primarily the D1 antagonist action of clozapine that accounts for its inability to cause tardive dyskinesia as well as its therapeutic effect in tardive dystonia. Regardless of its mechanism of action, the sustained improvement observed in this case suggests that clozapine should be tried in cases of severe refractory tardive dystonia.

Behavioral intervention to reduce water intake in the syndrome of psychosis, intermittent hyponatremia, and polydipsia

We describe a non-intensive behavioral intervention using an A-B design with extended follow-up on an open psychiatric unit to reduce water intake in a 52-year-old man with the syndrome of psychosis, intermittent hyponatremia, and polydipsia. A reinforcement schedule contingent upon weight gain secondary to water intake was employed. Mean diurnal weight gain was 7.1 pounds during a 23-week baseline which dropped to 4.1 pounds following 23 weeks of treatment and at a 1-year follow-up. Estimated fluid consumption dropped from 10 liters to 4 liters daily and incidents of hyponatremia decreased by 62%.

Clozapine-induced weight gain: prevalence and clinical relevance

OBJECTIVE

The aim of this study was to determine the prevalence and clinical relevance of weight gain during clozapine treatment. Previous reports indicated clinically significant weight gain in 13% to 85% of patients and an average gain of 9.0 to 24.7 lb.

METHOD

Twenty-one state hospital patients with treatment-resistant schizophrenia or schizoaffective disorder were weighed weekly for 12 weeks before clozapine treatment and during the first 16 weeks of treatment. Psychiatric symptoms were rated with a modified version of the Brief Psychiatric Rating Scale (BPRS).

RESULTS

The mean weight gain for the entire group was 13.9 lb, or 8.9% of body weight. During the 16 weeks of clozapine treatment, 38% of the patients experienced marked weight gains and 29% had moderate weight gains. The improvements in BPRS total score and composite negative symptom score were significantly greater for the eight patients with marked weight gains than for the other 13 patients.

CONCLUSIONS

Clozapine's propensity to induce weight gain may relate to the drug's efficacy and/or its unique neuropharmacologic effects. Increased attention to this phenomenon is important because of the morbidity associated with obesity.