Isolated abducens nucleus damage due to histiocytosis X. Electro-oculographic analysis and physiological deductions.

A case of complete rightward conjugate gaze paralysis, with electro-oculographic recordings, is reported. The only additional feature on clinical examination was a right infranuclear facial paresis. Radiographs of the chest showed multiple infiltrates in both lung fields; lung biopsy with ultrastructural study led to the diagnosis of histiocytosis X. A CT scan showed a single small tumour-like lesion, hyperdense and clearly defined, lying centrally in the fourth ventricle with a small ventral extension located just to the right of the midline. With appropriate treatment all the clinical signs rapidly subsided, together with the disappearance of the right ventral extension of the lesion visible on the CT scan. The clinical and CT scan data suggested that the initial parenchymatous damage almost exclusively involved the right abducens nucleus, a structure which is very rarely affected in an isolated manner. Both main clinical features of the abducens nucleus syndrome which distinguish it from the recently described paramedian pontine reticular formation syndrome were present, namely absence of all ipsilateral conjugate movements and persistence of ipsilaterally directed saccades in the contralateral hemifield of movement. Furthermore, differences between peak velocities of both eyes in oculocephalic movements suggested that a pathway analogous, at least functionally, to the ascending tract of Deiters described in the cat and in the monkey may exist in man. Lastly, some recent clinical data concerning this unusual cause of CNS damage are briefly reviewed.