1 + 1/2 syndrome

Question 1

1.5 description

Answer 1

Paralytic pontine exotropia

Consists of a unilateral Internuclear Ophthalmoplegia (INO) and ipsilateral horizontal gaze palsy.

Question 2

1.5 aetiology

Answer 2

Caused by an extensive caudal lesion in the pons, affecting the horizontal gaze center and the adjacent medial longitudinal fasciculus (MLF).
This lesion results in a palsy of both medial rectus muscles and one lateral rectus (gaze palsy plus INO).
Causes include demyelination, vascular issues, tumor, and inflammation.

Question 3

1.5 features

Answer 3

Main Clinical and Diagnostic Features:
Only remaining horizontal movement is abduction by the unaffected lateral rectus, associated with typical abducting nystagmus.

When the patient attempts to fixate with this eye in the primary position, the nystagmus will reduce or cease.

horizontal nystagmus more apparent in contralteral abducting eye

This results in a palsy of conjugate gaze on one side and an INO on looking to the other side. XOT.

Patients may adopt a marked abnormal head posture to achieve fixation with the preferred eye.

VOR may be preserves + overcome limitation of palsy

diplopia, blurred vision and oscillopsia.

Question 4

1.5 mx

Answer 4

Mx: Image motion on lateral and vertical gaze can result from gaze-evoked, up-beat, down-beat and torsional nystagmus; sector occlusion to spectacle lenses may reduce symptoms.

Question 5

why caution when using Hess chart in 1.5

Answer 5

Care must be taken when interpreting the Hess chart, as synergist muscles are affected in patients with lesions involving the horizontal gaze center as well as the MLF (partial one-and-a-half syndrome).
Since the Hess chart compares the action of synergistic muscles, it may compare abnormal with abnormal and miss the gaze palsy element.