Aktuelle Neurologie 2007; 34 - P795
DOI: 10.1055/s-2007-988064

Differentiation of internuclear ophthalmoplegia and myasthenic pseudo-internuclear ophthalmoplegia by subjective visual vertical

H Neugebauer 1, A Zwergal 1, T Brandt 1, M Strupp 1
  • 1München

Objectives: Internuclear ophthalmoplegia (INO) is characterized by an adduction deficit on lateral gaze and a dissociated nystagmus of the abducting eye. In the majority of cases INO occurs with lesions of the medial longitudinal fascicle (MLF) caused by multiple sclerosis or ischemia. However, extraocular muscle weakness in myasthenia gravis (MG) can mimic this ocular motor pattern and has been referred to as pseudo-internuclear-ophthalmoplegia (pseudo-INO). Differentiation between these entities can be difficult but is crucial for choosing specific therapeutic strategies. We here report that measurement of the subjective visual vertical (SVV) reliably differentiates INO from pseudo-INO.

Methods: In a retrospective study 10 patients with a unilateral pseudo-INO due to MG were compared with a control group of 15 patients with unilateral INO due to CNS disease. All patients underwent a detailed neuro-ophthalmological examination and thin-slice magnetic resonance imaging (MRI) of the brainstem. Acetylcholine-receptor (AChR) antibody titer testing and the Tensilon test were done, if a myasthenic origin of INO was suspected.

Results: Only 50% of myasthenic patients with the presentation of pseudo-INO showed positive AChR antibodies and 60% a positive Tensilon test. Brainstem lesions could not be excluded definitely in 20% of pseudo-INO cases in MRI. Taken together initially more than 30% of myasthenic pseudo-INO cases remained diagnostically uncertain. In these patients the diagnosis of MG was established later in the course of the disease. In the control group of INO, only 70% showed characteristic unilateral MLF lesions on MRI. The others could be diagnosed only on the basis of subtle additional central ocular motor findings (vertical nystagmus of small amplitude in the scanning laser ophthalmoscopy, low-grade skew deviation). Thus none of the common diagnostic tests had satisfactory selectivity that allowed reliable differentiation of pseudo-INO from INO. However as the major result of this study, it could be shown, that all patients with INO had pathological deviations of the SVV (from true verticality) to the contralateral side (mean: 5.3; range: 2.5–13) whereas none of the patients with pseudo-INO had SVV values out of the normal range (mean: 1.1, range: -1.8–2.3).

Conclusions: Measurement of SVV had a discriminatory power of 100% for the separation of pseudo-INO and INO and therefore provides a new reliable clinical tool for differential diagnosis.