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 Table of Contents  
CLINICAL CHALLENGE
Year : 2020  |  Volume : 32  |  Issue : 3  |  Page : 311-314

Unilateral abducent nerve palsy in a diabetic patient with treated cerebellopontine angle tumor


Department of Ophthalmology, Chaithanya Eye Institute, Kochi; Vettam Eye Clinic, Mulanthuruthy, Ernakulam, Kerala, India

Date of Submission24-Oct-2020
Date of Acceptance25-Oct-2020
Date of Web Publication23-Dec-2020

Correspondence Address:
Dr. Sanitha Sathyan
Vettam Eye Clinic, Perumpilly, Mulanthuruthy, Ernakulam - 682 314, Kerala
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/kjo.kjo_166_20

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  Abstract 


Isolated abducent nerve palsy in a diabetic patient with a history of treatment for cerebellopontine angle tumor poses challenges with regard to clinical diagnosis and management. This case discusses the challenges in clinching the diagnosis clinically, the need for imaging, and the guidelines for management.

Keywords: Cerebellopontine angle tumor, cerebellopontine angle meningioma, diabetic mononeuropathy, meningioma recurrence, unilateral abducent nerve palsy


How to cite this article:
Sathyan S. Unilateral abducent nerve palsy in a diabetic patient with treated cerebellopontine angle tumor. Kerala J Ophthalmol 2020;32:311-4

How to cite this URL:
Sathyan S. Unilateral abducent nerve palsy in a diabetic patient with treated cerebellopontine angle tumor. Kerala J Ophthalmol [serial online] 2020 [cited 2021 Jan 18];32:311-4. Available from: http://www.kjophthal.com/text.asp?2020/32/3/311/304548




  Introduction Top


Cerebellopontine angle (CPA) tumors are usually slow-growing masses and are diagnosed based on the characteristic symptomatology and brain imaging findings. Mononeuropathy presenting as unilateral abducent nerve palsy is a relatively common occurrence in long-standing diabetes mellitus. In a scenario in which a diabetic patient with a history of treatment for CPA tumor presents with unilateral abducent nerve palsy, clinical decision-making becomes difficult. This clinical query section discusses pertinent points regarding the diagnosis, brain imaging, and line of management in one such case.


  Panelists Top


  1. Dr. M V Francis, Chief Consultant, Teresa Eye and Migraine Center, Cherthala, Alleppey, Kerala
  2. Dr. Thomas Arun Varghese, Consultant in Glaucoma and Neuro-ophthalmology, Alphonsa Eye Hospitals, Pala, Thodupuzha, Kerala


  3. St Joseph Eye Hospital, Kanjirapally, Kerala

    Alexander Eye Centre, Ernakulam, Kerala

  4. Dr. Natasha Radhakrishnan, Professor, Amrita Institute of Medical Sciences, Kochi, Kerala.



  Case Top


A 54-year-old female presented with doubling of images on looking toward the left side for the past 1-week duration. She was diagnosed of diabetes mellitus (Type-2), 35 years back and was on oral hypoglycemic agents for the past 20 years. For the past 15 years, she is on insulin injections, but her diabetic status remains poorly controlled. She was diagnosed of hypertension and hyperlipidemia 30 years back and is on oral medications since then. She was diagnosed of meningioma of left CPA 3 years back following investigations for “ringing sensation” in the left ear. She underwent gamma knife irradiation for the same and had relief of symptoms after the treatment. She has had two episodes of binocular double vision 7 and 5 years back, for which she was treated conservatively and was symptom free after 6 months. There was no history of trauma, headache, ringing in the ears, vertigo, nausea/vomiting or blurred vision associated with the current episode.

Now, she presented with doubling of images on looking toward the left side and occasionally in the straight gaze. The double vision is more for distance and no doubling is reported while reading or watching television.

On examination, her unaided visual acuity was 6/12 in both the eyes. With –1.25 D cylinder at 70° and + 2.50 D near addition, she is improving to 6/6, N6. There is no abnormal posturing of the head, ptosis, or nystagmus. Corneal reflex test is central. There is limitation of abduction in the left eye (−2), and the pupils are normal. Saccades and pursuits are normal except for limitation of abduction in the left eye. Corneal sensation: Normal, color vision (Ishihara isochromatic test plates, Farnsworth D 15 test: normal, and there is no red desaturation in the left eye. Humphrey visual fields 30-2: Normal. Diplopia charting: no diplopia elicited in any position of gaze, including levoversion. Anterior segment examination shows grade: 1 nuclear sclerosis in both eyes, dilated fundus: disc normal, mild nonproliferative diabetic retinopathy changes present, and no clinically significant macular edema. General examination, neurological examination, and other systems: Normal.

Magnetic resonance imaging (MRI) brain (3.0 Tesla) done in 2017, post gamma knife radiation therapy, revealed a well-defined extra-axial dural mass of intermediated signal in T1-weighted image (WI) and T2-W1 and hyperintense signal in fluid-attenuated inversion recovery measuring 2.5 cm × 1.5 cm × 2 cm, involving the posterior margin of the petrous temporal bone on the left side [Figure 1]. The lesion showed a cerebrospinal fluid (CSF) cleft around it and was intending the pons and cerebellum on the left side and was covering the medial end of the external auditory meatus on the left side. No extension to the external auditory meatus, hydrocephalus, or encasement of the basilar artery was noted. These features were suggestive of meningioma of the left CPA.
Figure 1: Magnetic resonance imaging of the brain showing the lesion in the cerebellopontine angle

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Three follow-up MRIs done at 6-monthly intervals showed no significant changes in the size and morphology of the left cerebellopontine angle meningioma.

Queries

1. What is the possible diagnosis? Left abducent nerve paresis due to diabetic mononeuropathy or due to worsening of CPA meningioma?

Dr. M V Francis

Vasculopathic cranial neuropathy is the most common cause of isolated unilateral sixth nerve deficit in individuals over age 50. Extracting all the pivotal points from the history, my tentative diagnosis is left abducent nerve palsy due to diabetic mononeuropathy. Salient diagnostic points are as follows:

  • Typical age of presentation and the presence of long-standing diabetes mellitus, which is poorly controlled
  • Two more additional vascular risk factors in the form of long-standing systemic hypertension and hyperlipidemia
  • Two episodes of binocular diplopia in the past with an interval of 2 years, with complete recovery within 6 months of conservative treatment
  • No other Vestibulo-cocchlear symptoms suggestive of worsening of CPA meningioma, with no significant change in size and morphology as per the follow-up MRIs
  • Her first diagnostic symptom at diagnosis was tinnitus, and a recurrence or further growth will be usually present with tinnitus or hearing loss. However, no symptoms suggestive of CPA tumor recurrence such as paresthesia in the distribution of trigeminal nerve, facial twitching, reduced corneal sensation, or Brun nystagmus, occurred during the present episode. The combination of these factors indicates that worsening of CPA tumor is unlikely in this patient.


Dr. Thomas Arun Varghese

Isolated abducent nerve palsy in a person with systemic comorbidities is usually attributed to vascular risk factors. However, in patients with other intracranial or ocular pathology, pointing out the exact cause becomes pertinent.

A diabetic patient with poor control is a high-risk candidate for acquiring a mononeuropathy. In a large Indian study on isolated abducent nerve palsies, 54.70% were attributed to vasculopathic factors after ruling out other causes through appropriate imaging.[1] In a patient with a history of CPA tumor treated with gamma knife irradiation 3 years prior, recurrence of the tumor is a definite possibility which can only be ruled out by a repeat neuroimaging. Clinical features suggestive of recurrence would be recent-onset involvement of other cranial nerves such as reduction in corneal sensation, which was previously normal, nystagmus, or mild facial palsy.

Some of the hypotheses regarding relapsing and remitting course of abducent nerve palsy are the following:

  1. Compression, sometimes intermittent, by a mass causing demyelination followed by remyelination[2]
  2. Neuropraxia: Segmental demyelination often triggered by trivial trauma in an already-stretched nerve
  3. Thickening and hyalinization of nutrient vessels, leading to focal ischemic demyelination followed by remyelination. This is the likely mechanism in vasculopathic cases.[3]


As can be understood from mechanisms (1) and (2), mass lesions can also cause abducent nerve palsy, which usually recovers. Meningiomas, which are slow-growing tumors, can cause gradual stretching of the nerve. The past history of abducent nerve palsy 7 and 5 years back, may have been due to neuropraxia of a stretched nerve which had recovered.

Dr. Natasha Radhakrishnan

The most likely diagnosis appears to be diabetic mononeuropathy in view of the uncontrolled blood sugars and the previous two episodes which recovered on conservative management. The points against worsening of CPA tumor are the lack of characteristic symptoms such as deafness and tinnitus. Furthermore, corneal sensation is normal and there is no evidence of papilledema. However, given the history of treatment for meningioma, I would repeat imaging to confirm that the tumor has not increased in size.

Queries

2. What is your approach toward suspected diabetic mononeuropathy? Will you offer intravenous steroids to the patient in view of a possible diabetic mononeuropathy or choose to observe the patient?

Dr. M V Francis

As we know, symptomatic diplopia in diabetic mononeuropathy will improve on its own within 3–6 months, like the past two attacks in the patient. There is no need of any intervention at present, and only observation is enough with careful 2-weekly or monthly follow-up. The most important factor in management is strict control of diabetes mellitus by a physician/diabetologist/endocrinologist. Intravenous steroids are not indicated as her diabetes is poorly controlled. With proper control of diabetes, recovery will be almost complete within 3–6 months. Furthermore, the patient is to be taught self-monitoring of her hearing with finger rubbing test. In case of any suspicion, an otorhinolaryngological reference and audiometry are to be done.

Dr. Thomas Arun Varghese

As the mechanism is usually ischemia, I will observe the patient and liaise with the treating physician to improve the control of diabetes mellitus. I usually monitor the patient weekly for the first 2 weeks and will look for any other new-onset neurological involvement. If the patient is stable or improving, further follow-ups may be done once fortnightly. Symptomatic measures such as occlusion are advised during this period.

Dr. Natasha Radhakrishnan

I will not consider intravenous steroids as diabetic mononeuropathy is a self-limiting condition. I would ask the patient to achieve better control of diabetes mellitus and would follow-up the patient monthly. Monitoring of pupils, corneal sensation, fundus, and development of any other cranial nerve palsy will be done at each visit, even if the diagnosis is diabetic mononeuropathy. I expect full recovery in 3–4 months.

Queries

3. What is your approach toward suspected CPA tumors? Will you ask for imaging directly or refer to a neurologist before imaging? If you ask for imaging, what will be your investigation of choice?

Dr. M V Francis

If worsening of CPA lesion is suspected with very early symptoms and signs discussed above or if abduction deficit is persisting after 3 months of observation and good control of vascular risk factors, I will image this patient on my own to confirm my suspicion of worsening of CPA tumor. If the imaging indicates worsening of the tumor, I will refer her to the same center where gamma knife stereotactic radiosurgery was done previously. My choice of imaging will be in discussion with the radiologist/neuroradiologist as radiographic investigations of the skull base and posterior fossa (PF) can be challenging. Standard computed tomography sequences have poor resolution in this region due to signal degradation at soft tissue-to-bone interfaces. Magnetic resonance images are not hampered by this limitation. Contrast-enhanced MRI is the most sensitive investigation in the evaluation of CPA lesions. Ideally, imaging must include high resolution (1.5/3 Tesla), T2 weighted, three dimensional MRI. This sequence is currently the MRI technique of choice for CSF cisternography for visualizing the CSF spaces at the skull base and thus the cranial nerves, the Meckel's caves, the internal auditory canals, and the fluid within the inner ear structures.

Dr. Thomas Arun Varghese

When CPA mass is suspected due to other symptoms and signs in addition to abducent nerve palsy, I will request for MRI brain with contrast with a detailed letter to the radiologist. Referral to the neurologist will be based on the report.

In majority of cases of recurrent abducent nerve palsy, there is a definite cause such as compressive[4],[5] (aneurysm, tumor) or vasospasm.[5] Appropriate and sometimes repeat imaging will pick up the cause in most cases.

Dr. Natasha Radhakrishnan

In a patient with suspected diabetic mononeuropathy, if I need to do an MRI to rule out intracranial pathology, I would order an MRI myself. However, in this patient with the history of a meningioma and gamma knife surgery, I would liaise with the treating neurologist or neurosurgeon before ordering MRI. MRI brain with contrast would be my preferred imaging modality.


  Summary Top


In this case, all the panelists have agreed upon the first provisional diagnosis as diabetic mononeuropathy, due to its high prevalence, absence of characteristic symptoms associated with CPA tumor, and documented stable lesion in serial MRIs. However, due to the multiple clinical factors involved, two of the panelists would also suggest an MRI brain at the presentation itself to rule out the possible increase in tumor size and subsequent compression. One of the panelists would observe the patient closely for any symptom/sign indicative of cerebellopontine tumor. He would suggest imaging only if any such symptoms/signs appear or if abduction deficit is persisting after 3 months of observation and good control of vascular risk factors.

MRI of the brain is the preferred imaging modality and the specifications would be decided in consultation with a radiologist/neurologist/neurosurgeon. All the panelists would manage isolated diabetic neuropathy cases with observation and close follow-ups. This is to rule out new-onset symptoms/cranial nerve involvements, and monocular occlusion will be offered for symptomatic diplopia. Control of vascular risk factors such as diabetes mellitus, hypertension, and hyperlipidemia would be done in consultation with the physician/endocrinologist and it is expected that the isolated diabetic abducent nerve palsy would resolve within 6 months.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initial s will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Nair AG, Ambika S, Noronha VO, Gandhi RA. The diagnostic yield of neuroimaging in sixth nerve palsy-Sankara Nethralaya Abducens Palsy Study (SNAPS): Report 1. Indian Journal of Ophthalmology. 2014;62:1008.  Back to cited text no. 1
    
2.
Blumenthal EZ, Gomori JM, Dotan S. Recurrent abducens nerve palsy caused by dolichoectasia of the cavernous internal carotid artery. Am J Ophthalmol 1997;124:255-7.  Back to cited text no. 2
    
3.
Asbury AK, Aldredge H, Hershberg R, Fisher CM. Oculomotor palsy in diabetes mellitus: A clinico-pathological study. Brain 1970;93:555-66.  Back to cited text no. 3
    
4.
Nguyen DQ, Perera L, Kyle G. Recurrent isolated sixth nerve palsy secondary to an intracavernous carotid artery aneurysm. Eye (Lond) 2006;20:1416-7.  Back to cited text no. 4
    
5.
Chan JW, Albreston J. Causes of isolated recurrent ipsilateral abducent nerve palsy in older adults: A case series and review of literature. Clin Ophthalmol 2015;9:373-7.  Back to cited text no. 5
    


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