Neurological evaluation of acute vertical diplopia

Abstract

Acute vertical diplopia requires an immediate neurological evaluation. The preliminary differential diagnosis is based on a few basic questions, which can be answered by simple clinical tests. The neurologist determines whether the lesion affects the optic, ocular motor, or vestibular system, and confirms that the problem is neural. Otherwise the patient is referred to the ophthalmologist. A thorough neurological assessment then allows concluding whether the lesion is within the central nervous system or peripheral. Photographs of the ocular fundus on both sides help to distinguish between trochlear nerve palsy and ocular tilt reaction or skew torsion. For a finer differential diagnosis, focused MR-imaging is always needed. The diagnosis of an optic disorder should be considered if the vertical diplopia is clearly monocular. If vertical diplopia is binocular, the neurologist first searches for typical oculomotor (III) or trochlear nerve (IV) palsies. While III-palsy is mostly due to ischaemia (pupil typically spared) or compression (pupil typically affected) of the nerve, IV-palsy is mostly due to head trauma. III- and IV-palsies that go together with retroorbital pain should lead to a careful evaluation for neoplasm, thrombosis, and inflammation of the cavernous sinus. One can never be absolutely sure whether a typical III- or IV-palsy is due to a problem along the nerve or within the brainstem, except if other signs clearly indicate a lesion within the ipsilateral orbit or cavernous sinus. Thus neuro-imaging should always include MR-imaging of the midbrain to detect lesions in the nuclei and fascicles of the oculomotor and trochlear nerves. If a suspected III-palsy does not include all of the four corresponding extraocular muscles (superior, inferior, and medial recti; inferior oblique), one should also consider myasthenia gravis, which can mimic any neural extra-ocular muscle palsy. Wernicke's disease is always a valid differential diagnosis of binocular vertical diplopia, especially in the presence of pathological nystagmus and ataxia. If binocular vertical diplopia is associated with deficits of multiple cranial nerves, one should consider a demyelinating disease such as Miller-Fisher and Guillain-Barre syndrome. Skew deviation is a vertical misalignment of the two eyes resulting from disturbance of supranuclear inputs to the ocular motor neurons of the vertical-torsional eye muscles. If skew deviation goes together with ocular torsion towards the lower eye, so-called skew torsion, an imbalance in the vestibular system, mainly a unilateral lesion of pathways, which combine otolith and vertical semicircular canal signals, is likely. Skew torsion combined with head roll towards the lower eye forms the triad of ocular tilt reaction (OTR). Consistent with the anatomy of the graviceptive pathways, ipsiversive skew torsion (ipsilateral eye lower, and ipsilateral binocular torsion) and ipsilateral OTR (ipsiversive skew torsion, and ipsilateral head tilt) will occur as a result of unilateral peripheral or pontomedullary lesions below the pontine crossing of the graviceptive pathways. In contrast, a unilateral pontomesencephalic brainstem lesion leads to contraversive skew deviation (contralateral eye lower) and contralateral OTR (contraversive skew deviation, contralateral binocular torsion, and contralateral head tilt).