Convergence spasm in conversion disorders: prevalence in psychogenic and other movement disorders compared with controls.
BACKGROUND
Convergence spasm refers to transient ocular convergence, miosis and accommodation associated with disconjugate gaze mimicking abducens palsy. While it may be a manifestation of brainstem pathology, this sign is often associated with conversion (somatisation) disorders and, if unrecognised as a sign of a psychogenic disorder, it may lead to unnecessary and occasionally invasive evaluation.


METHODS
To better characterise this neuro-ophthalmologic sign, 36 subjects were studied, 13 with psychogenic movement disorders, 11 with organic movement disorders and 12 normal controls. Patients were recorded during a manoeuvre to elicit convergence spasm and the videotapes were rated by two blinded raters on a scale of 0=normal, 1=mild convergence spasm and 2=marked convergence spasm.


RESULTS
Convergence spasm was present in 9/13 (69%) psychogenic movement disorders cases, 4/11 (36%) non-psychogenic movement disorders cases and 4/12 (33%) controls (p=0.049 when psychogenic vs non-psychogenic disorders or controls were compared). Inter-rater reliability analysis of the presence (rating 1 or 2) versus absence (rating 0) showed good agreement (27/36 or 75%; kappa 0.491, SE 0.141, p=0.002). Analysis for the presence of marked convergence spasm (rating 2) yielded agreement in 32/36 (88.9%) examinations (kappa 0.652, SE 0.154, p<0.001) with a specificity of 87% (sensitivity 15%).


CONCLUSION
Convergence spasm may provide benefit in the clinical examination of psychogenic movement disorders patients.