Convergence spasm with miosis and accommodative blurring is a positive functional sign, and the clustering of functional symptoms is characteristic: patients commonly have several functional symptoms at once, including tremor, weakness, sensory disturbance, fatigue and pain, and about a third of neurology outpatients have symptoms that are only somewhat or not at all explained by disease. Recognizing the cluster allows a single unifying explanation to be offered and stops the diagnostic cascade.
Extensive negative testing has already been done, and the marginal yield of catheter angiography in an alert patient with normal magnetic resonance imaging, normal opening pressure and a demonstrable positive sign is essentially nil, while the procedural risk is real. Investigations in this setting also carry a nocebo cost: each new test reinforces the patient belief that a hidden disease is being missed and makes subsequent acceptance of the diagnosis harder. The principle is to investigate appropriately once, then explain positively.
On the ABPN blueprint this item maps to the Clinical aspects of neurologic disease axis, because the competency tested is integrating multiple symptoms into one recognized clinical syndrome. Note that a functional diagnosis does not license dismissing new or changing symptoms; comorbid disease occurs and each new complaint deserves proportionate assessment.
Incorrect Answers
- A. Angiography and repeat manometry are not needed when a positive sign is demonstrated and prior imaging and pressure measurement were normal.
- B. Functional symptoms frequently coexist with genuine disease, so blanket attribution of every symptom without assessment risks missing treatable comorbidity.
- C. The presence of one functional symptom raises rather than lowers the probability that another unexplained symptom is also functional.
- E. Ocular myasthenia spares the pupil entirely, and his acetylcholine receptor antibody testing was already normal in a context with no ptosis or fatigability.
Testing Pearls
- Functional symptoms cluster; finding one raises the probability that another is also functional.
- About a third of neurology outpatients have symptoms not or only somewhat explained by disease.
- Repeated investigation carries a nocebo cost and undermines acceptance of the diagnosis.
- A functional diagnosis does not exempt new or changing symptoms from proportionate assessment.
- Pupil involvement excludes myasthenia gravis as a cause of ocular motility disturbance.
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.
- Espay AJ, Aybek S, Carson A, Edwards MJ, Goldstein LH, Hallett M, et al. Current concepts in diagnosis and treatment of functional neurological disorders. JAMA Neurol. 2018;75(9):1132-1141.
