The combination of apparent limitation of abduction, simultaneous adduction of the fellow eye, miosis and accommodative blurring is the triad of convergence spasm. The pupillary constriction is the giveaway: the near response is a synkinesis of convergence, accommodation and miosis, so miosis occurring at the moment abduction fails proves that the eyes are converging rather than that an abducens nerve is failing. Full ductions on monocular testing and the transient, fluctuating nature of the episodes complete the picture.
Convergence spasm may occasionally be a manifestation of dorsal midbrain or posterior fossa pathology, but in the outpatient setting it is most often functional. In a controlled study that videotaped a standardized manoeuvre, convergence spasm was seen in 69 percent of patients with psychogenic movement disorders compared with 36 percent of those with organic movement disorders and 33 percent of controls, and marked convergence spasm had a specificity of about 87 percent with low sensitivity. It is therefore a useful confirmatory rather than screening sign, and it must be read together with the miosis.
This is solid PGY-3 and PGY-4 neuro-ophthalmology, placing the item at the Intermediate level of RITE content. Recognizing the sign spares the patient an unnecessary work-up for raised intracranial pressure or brainstem disease.
Incorrect Answers
- A. An abducens palsy causes constant, not intermittent, limitation of abduction, does not produce miosis, and would persist on monocular duction testing.
- B. Internuclear ophthalmoplegia limits adduction of the eye ipsilateral to the medial longitudinal fasciculus lesion with abducting nystagmus in the fellow eye, and convergence is characteristically preserved.
- C. Ocular myasthenia produces fatigable ptosis and variable ocular misalignment without pupillary involvement, and the pupil is always spared.
- D. One-and-a-half syndrome combines an ipsilateral horizontal gaze palsy with an internuclear ophthalmoplegia and produces a fixed rather than an episodic deficit.
Testing Pearls
- Convergence spasm mimics abducens palsy but is accompanied by miosis and accommodative blurring.
- Pupillary constriction during failed abduction distinguishes spasm of the near reflex from nerve palsy.
- Ductions are full when each eye is tested monocularly in convergence spasm.
- Marked convergence spasm is specific but insensitive for functional movement disorders.
- Rarely, convergence spasm reflects dorsal midbrain or posterior fossa disease.
References
- Jankovic J, Mazziotta JC, Newman NJ, Pomeroy SL, editors. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022. p. 2084.
- Fekete R, Baizabal-Carvallo JF, Ha AD, Davidson A, Jankovic J. Convergence spasm in conversion disorders: prevalence in psychogenic and other movement disorders compared with controls. J Neurol Neurosurg Psychiatry. 2012;83(2):202-204.
- Stone J. Functional neurological disorders: the neurological assessment as treatment. Pract Neurol. 2016;16(1):7-17.
