Neurological Department, Klinikum Worms, Germany The spectrum of ocular motor abnormalities as the only clinical sign of brain stem lesions Frank Thömke Neurological Department, Klinikum Worms, Germany The widespread use of magnetic resonance imaging has shown an increasing variety of monosymptomatic brain stem lesions, mainly infarcts. Among them, ocular motor abnormalities represent an important subgroup. This paper reviews the spectrum of such abnormalities. Possible ocular motor abnormalities as the only clinical signs of brainstem lesions isolated 3rd nerve palsies due to midbrain infarcts isolated superior rectus palsy due to a midbrain infarct Kwon et al. Arch Neurol 2003 isolated inferior rectus palsy due to a midbrain infarct Lee & Kim Neurology 2006 isolated superior oblique palsy due to a midbrain infarct Walsh Arch Neurol 2010 isolated painful mydriasis due to a midbrain abscess  3rd nerve palsy „superior branch“ palsy „inferior branch“ palsy rectus superior palsy rectus inferior palsy rectus medialis palsy unilateral mydriasis unilateral mydriasis + ptosis  4th nerve palsy  6th nerve palsy  vertical gaze palsy  crossed vertial gaze palsy  monocular elevation paresis  horizontal gaze palsy  imternuclear ophthalmoplegia  1½-syndrome  8½-syndrome  skew deviation  ocular tilt rection  horizontal-rotatory nystagmus  upbeat nystagmus  Horner‘s syndrome INC riMLF riMLF III IV isolated vertical gaze palsy due to a midbrain infarct isolated monocular elevation palsy due to a midbrain infarct Thömke & Hopf Brain 1992 VI isolated horizontal gaze palsy due to a pontine infarct isolated INO due to a pontine infarct Nucl. Intercalatus (Staderini) Hassler Neurology 1967 isolated 1½ - syndrome due to a pontine infarct isolated 8½ - syndrome (1½-syndrome + 7th nerve palsy) due to a pontine infarct isolated pseudoneuritis vestibularis due to a medullary infarct isolated pseudoneuritis vestibularis due to a medullary demyelination upbeat nystagmus + vertigo due to a medullary demyelination isolated 6th nerve palsy due to a Gd-enhancing pontine demyelination isolated 6th nerve palsy due to a pontine infarct Except where indicated all MRI-images are with kind permission of W. Müller-Forell and P. Stoeter, Institue for Neuroradiology, University Medical Center Mainz, Germany There are 4 main groups of brainstem lesions, which cause isolated ocular motor abnormalities:  Lesions of infranuclear ocular motor nerve segments cause 3rd, 4th and 6th nerve palsies.  Lesions affecting nuclei related to eye movements (3rd and 6th nerve nucleus, riMLF, INC, nucleus intercalatus Staderini) are followed by horizontal and vertical gaze palsies or upbeat nystagmus.  Lesions interrupting internuclear connections may cause internuclear ophthalmoplegia, monocular elevation paresis, skew deviation, ocular tilt reaction or upbeat nystagmus.  Combined lesions of nuclear and internuclear or infranuclear structures are the anatomical basis of 1½-syndrome, 8½-syndrome, or horizontal gaze palsy with facial palsy. The clinical significance of these disorders is not known.