The so-called one-and-a-half syndrome, type II: a new syndrome?

Abstract

Objective: The term one-and-a-half syndrome, type II, was recently coined and has been applied to two somewhat different eye movement disorders: the loss of voluntary horizontal eye movements except for adduction in one eye (one patient with two lesions, one in the cerebral hemisphere and the other in the cavernous sinus) and the loss of all voluntary horizontal eye movements with adduction nystagmus in the right eye on attempted gaze to the left and preserved abduction in both eyes with the doll’s head maneuver (one patient with infarction of the midbrain). The justification of the term ‘one-and-a-half syndrome, type II’ is questioned. Design: Retrospective analysis of 9000 consecutive electro-oculographic recordings (EOG) with respect to combined abnormalities of conjugated horizontal eye movements to one side and abduction to the other. Results: Only one patient had loss of horizontal eye movements sparing adduction in one eye on clinical examination. In eight patients with clinically unilateral abduction paresis, EOG disclosed slowing of contraversive saccades. Another eight patients with clinically unrestricted horizontal eye movements had EOG-documented unilaterally slowed abduction saccades and slowing of contraversive saccades. Masseter reflex was abnormal in five patients and blink reflex in three. MRI performed in eight and CT in three of these patients failed to disclose acute lesions. Conclusions: The combination of a horizontal gaze paresis to one side and abduction paresis to the other is very rare, even if partial and subclinical forms are included. It occurs with single pontine or mesencephalic lesions or with two lesions at different sites, and can be caused by different mechanisms. Such an eye movement disorder does not constitute a new syndrome, as it entails neither a constellation of clinical findings due to an anatomically well-localized lesion, nor a consistent constellation of signs and symptoms due to a disease process.