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

Objective: The term one-and-a-half syndrome, type II, was recently coined a nd has been applied to two somewhat different eye movement disorders: the l oss 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 moveme nts 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 pa tient 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 a nd abduction to the other. Results: Only one patient had loss of horizontal eye movements sparing adduction in one eye on clinical examination. In eig ht patients with clinically unilateral abduction paresis, EOG disclosed slo wing of contraversive saccades, Another eight patients with clinically unre stricted horizontal eye movements had EOG-documented unilaterally slowed ab duction saccades and slowing of contraversive saccades. Masseter reflex was abnormal in five patients and blink reflex in three. MRI performed in eigh t and CT in three of these patients failed to disclose acute lesions. Concl usions: The combination of a horizontal gaze paresis to one side and abduct ion paresis to the other is very rare, even if partial and subclinical form s are included. It occurs with single pontine or mesencephalic lesions or w ith two lesions at different sites, and can be caused by different mechanis ms. Such an eye movement disorder does not constitute a new syndrome, as it entails neither a constellation of clinical findings due to an anatomicall y well-localized lesion, nor a consistent constellation of signs and sympto ms due to a disease process.