Acquired Third Nerve Palsy and a Case of Reversed Anisocoria

AUTHORS:
Jonathan C. Tsui, MD • Nisarg Joshi, MD • Justin Etzel, MD • Christopher Whiting, DO

AFFILIATIONS:
Geisinger Medical Center, Danville, Pennsylvania

CITATION:
Tsui JC, Joshi N, Etzel J, Whiting C. Acquired third nerve palsy and a case of reversed anisocoria. Consultant. 2021;61(7):e22-e23. doi:10.25270/con.2020.10.00012

Received May 26, 2020. Accepted September 22, 2020. Published online October 7, 2020.

DISCLOSURES:
The authors report no relevant financial relationships.

CORRESPONDENCE:
Jonathan C. Tsui, MD, Geisinger Woodbine Lane, 16 Woodbine Ln, Danville, PA 17821 (jctsui@geisinger.edu)

Third nerve palsy is a potentially fatal ophthalmic presentation that can lead to significant morbidity and mortality if it is not recognized promptly. Common symptoms include diplopia, ptosis, and blurred vision, but symptoms can often be vague and associated with nonspecific presentations. Any patient presenting with diplopia should be evaluated to determine whether the diplopia is monocular or binocular, with binocular diplopia indicating a higher potential for a severe neurologic comorbidity. This is easily determined by asking the patient whether or not the diplopia resolves when covering either eye. In addition, extraocular motility, confrontational visual fields, position of eyelids, and pupils can be evaluated in any outpatient primary care or urgent care setting without sophisticated equipment.¹

Case report. A 64-year-old man was seen for a 3-day referral in our outpatient ophthalmology clinic. The patient’s medical history was significant only for controlled hypertension; he denied having diabetes or hyperlipidemia. The patient noted that 5 days prior to presentation, he had begun experiencing painless binocular oblique diplopia (2 images displaced diagonally) with subjective worsened visual acuity in his right eye. He also had noted an associated mild headache. Four days prior to presentation, he had presented to an urgent care clinic noting these symptoms, as well as significant sinus pressure and discharge, and was diagnosed with diplopia, ptosis of the left eyelid, and alternating skew deviation on lateral gaze. The patient was advised to go to the emergency department (ED) for further workup, but the patient declined due to COVID-19 precautions. The outpatient laboratory workup at the urgent care clinic consisted of a complete blood cell count (CBC) and thyroid function tests, the results of which were unremarkable.

Upon presentation to the ophthalmology clinic, the patient was found to have a visual acuity of count fingers at 3 feet in the right eye and 20/50 in the left eye. The patient’s pupils demonstrated anisocoria. The left pupil measured 2.5 mm in light and 5 mm in the dark, while the right pupil measured 2 mm in light and 6 mm in the dark. Motility of the left eye was restricted with only preservation of abduction (Figure). The anterior segment examination demonstrated a hypermature cataract in the right eye and a normal anterior segment in the left eye. Dilated fundus examination revealed a poor view of the fundus of the right eye due to the cataract, and a normal fundus in the left eye.

Discussion. The oculomotor nerve (cranial nerve III) controls extraocular muscle function (superior rectus, inferior rectus, medial rectus, inferior oblique, and levator palpebrae superioris) and parasympathetic autonomic function (pupillary sphincter and ciliary muscles).² Damage to this nerve leads to dysfunction of the extraocular muscles (classically, an eye that is down-and-out) and ptosis. In addition, dysfunction of the pupillary sphincter may also be present, leading to ipsilateral mydriasis and anisocoria. In a complete third nerve palsy, all of the nerve’s functions are affected, and the pupils are irregular. In a partial third nerve palsy, only part of the nerve function is affected, more commonly the function of the extraocular muscles.²

The differential diagnosis of a third nerve palsy includes microvascular causes, vascular compression from an aneurysm or mass, temporal arteritis, myasthenia gravis, thyroid eye disease, demyelination, internuclear ophthalmoplegia, infectious etiologies, trauma, and other conditions.³ Given the potentially fatal implications of many third nerve palsy etiologies, prompt evaluation is indicated, especially if the pupils are abnormal. Yet, while the initial diagnosis is made by way of physical examination, studies have demonstrated that pupil involvement is not a reliable indicator of aneurysm presence, such that anisocoria, or lack thereof, in third nerve palsy does not rule out life-threatening differential diagnoses.^4,5 In fact, the pupillary examination in this patient’s case was confounded by other findings.

Due to the possibility of missing a fatal aneurysm, it is essential to promptly refer any patient with third nerve palsy, especially if pupils are irregular, for imaging studies, a CBC, erythrocyte sedimentation rate, C-reactive protein, and myasthenia gravis antibodies.¹ In the setting of a severe headache, a noncontrast computed tomography (CT) scan of the head should be performed expeditiously to rule out aneurysmal rupture and subarachnoid hemorrhage. In addition, all patients should undergo magnetic resonance imaging (MRI) of the brain and CT angiography/magnetic resonance angiography (MRA) of the head with attention to the brainstem and circle of Willis.³ The patient should be counseled on the life-threatening consequences of not undergoing emergent evaluation.¹ In addition, if a third nerve palsy diagnosis is not certain, a same-day referral or telephone call to an ophthalmology practice is indicated.

The evaluation of this patient was complicated by the presence of a mature cataract in the right eye, which caused a reversal of the expected anisocoria. Due to the cataract, less light was able to reach the retina, resulting in a relatively decreased pupillary constriction of the right eye at baseline. Thus, dilation of the left eye from the third nerve palsy did not produce the classic anisocoria.

At our recommendation, the patient was transferred to the ED for imaging and further laboratory testing. MRI/MRA did not show intracranial masses or aneurysmal compression, and this patient fared well. Bloodwork findings were similarly unremarkable. After discharge from the ED, the patient returned to the ophthalmology clinic for evaluation of the right fundus using ultrasonography, which revealed normal fundus anatomy. The patient was diagnosed with a microvascular third nerve palsy and will be observed for spontaneous improvement over the next 3 to 6 months.⁶ Interim treatment of diplopia includes patching the affected eye to decrease diplopia symptoms or prism modification to spectacles, depending on the severity of symptoms.¹

REFERENCES:

1. Isolated third nerve palsy. In: Bagheri N, Wajda BN, eds. The Wills Eye Manual: Office and Emergency Room Diagnosis and Treatment of Eye Disease. 7th ed. Wolters Kluwer; 2017:chap 10.5.
2. McDougal DH, Gamlin PD. Autonomic control of the eye. Compr Physiol. 2015;5(1):439-473. doi:10.1002/cphy.c140014
3. Lo C-P, Huang C-F, Hsu C-C, et al. Neuroimaging of isolated and non-isolated third nerve palsies. Br J Radiol. 2012;85(1012):460-467. doi:10.1259/bjr/38090653
4. Fang C, Leavitt JA, Hodge DO, Holmes JM, Mohney BG, Chen JJ. Incidence and etiologies of acquired third nerve palsy using a population-based method. JAMA Ophthalmol. 2017;135(1):23-28. doi:10.1001/jamaophthalmol.2016.4456
5. Keane JR. Third nerve palsy: analysis of 1400 personally-examined inpatients. Can J Neurol Sci. 2010;37(5):662-670. doi:10.1017/s0317167100010866
6. Roarty J. Third-nerve palsy. American Academy of Ophthalmology Pediatric Ophthalmology Education Center. September 28, 2017. Accessed September 23, 2020. https://www.aao.org/disease-review/third-nerve-palsy-2