A 3-year review of cranial nerve palsies from the University of Port Harcourt Teaching Hospital Eye Clinic, Nigeria.

PURPOSE: To provide the types, frequency and clinical information on common cranial nerve palsies seen at the Eye Clinic at the University of Port Harcourt Teaching Hospital.
MATERIALS AND METHODS: A chart review was performed of patients who presented with cranial nerve palsy at the Eye Clinic over a 3-year period (January 2009-December 2011). Data were collected on age, sex, type of cranial nerve palsy, a history of systemic disease such as diabetes mellitus (DM), hypertension and cerebrovascular disease. Exclusion criteria included medical charts with incomplete data. Data was analyzed using Epi-info Version 6.04D. Statistical significance was indicated by P < 0.05.
RESULTS: Twenty-four patients had cranial nerve palsies. There were 11 males and 13 females with a mean age of 34.50 ± 18.41 years. Four patients (26.6%) had exotropia while three patients (20%) had esotropia. Complete ophthalmoplegia was noted in two patients (13.3%). The 3(rd) and 6(th) cranial nerves were affected in seven patients each (29.2%) and five patients (20.8%) had 7(th) cranial nerve palsy. Approximately 38% of patients with cranial nerve palsies had systemic disorders (16.7% systemic hypertension; 12.5% DM). The relationship between cranial nerve palsy and systemic disorder was statistically significant (P < 0.01).
CONCLUSION: This is the first study in the literature on ocular cranial nerve palsies in Southern Nigeria. Third and sixth cranial nerve palsies were the most common cases to present to the University of Port Harcourt Teaching Hospital Eye Clinic. There was a statistically significant association to systemic disorders such as hypertension and DM and majority of cases with 6(th) cranial nerve palsy.

INTRODUCTION

Cranial nerve palsy is a form of palsy involving one or more of the cranial nerves. It may cause a complete or partial weakness or paralysis of the areas innervated by the affected nerve. Cranial nerve palsies can be congenital or the result of traumatic or vascular disorders (hypertension, diabetes mellitus (DM), stroke, aneurysms). They can also be due to infections, migraine headaches, tumors or elevated intracranial pressure. The age of the patient as well as clinical findings suggests the type of diagnostic tests required to determine the probable etiology. The 3rd, 4th and 6th cranial nerve palsies can limit eye movements and produce diplopia. The orientation of the diplopia is usually based on the affected cranial nerve. In addition to the limitation of eye movements, a 3rd nerve palsy can also cause ptosis or mydriasis. Some cranial nerve palsies are easy to identify because they affect eye movements or facial expression with resultant difficulty in controlling eye movements or engaging in facial expressions such as smiling. Some cranial nerve palsies resolve spontaneously, especially if they are due to microvascular causes such as DM and hypertension.

Of all ocular cranial nerve palsies, several authors have reported that 6th cranial nerve palsy was the most common, followed by the 3rd and then 4th cranial nerves.123 From these studies, the common causes of ocular cranial nerve palsies include head trauma, space-occupying lesions, and vascular lesions (DM, hypertension and atherosclerosis).2 In a cohort of 915 stroke patients, Rowe et al., reported ocular motor cranial nerve palsies in 10% of the patients.4 Most (58%) of the palsies involved the 6th nerve, followed by the 3rd (26%) and then the 4th cranial nerves (16%).4 They4 reported unilateral third nerve palsy in 23 patients (26%), unilateral fourth nerve palsy in 14 patients (16%) and unilateral sixth nerve palsy in 52 patients (58%). They4 found that the most common location of a stroke lesion causing cranial nerve palsy was the brainstem or cerebellum. They also reported that the presence of manifest strabismus was significantly higher in third and fourth nerve palsies than sixth nerve palsy.

This study provides clinical information and the frequency of the most common types of cranial nerve palsies evaluated at the University of Port Harcourt Teaching Hospital Eye Clinic and their association to systemic disorders.

MATERIALS AND METHODS

A retrospective chart review was performed of all patients with cranial nerve palsies who presented to the University of Port Harcourt Teaching Hospital Eye Clinic from January 2009 to December 2011. Data were collected and analyzed on age, sex, history of systemic disease such as diabetes mellitus, hypertension and cerebrovascular disease. The details of the systemic diseases were recorded from the patient charts. Ocular examination data were collected on the presenting symptoms and signs, visual acuity, range of extraocular motility and pupillary light reaction. Visual acuity was assessed with a Snellen chart.

Our diagnosis of cranial nerve palsy was mainly clinical and was based on the presenting symptoms and signs, which included severe headaches and fever, ptosis, diplopia, lagophthalmos, deviation of the mouth to one side, esotropia, exotropia, hypertropia or complete ophthalmoplegia. Computed tomography of the brain was performed in 9 patients; 8 were within normal limits and one showed an intracranial mass. Exclusion criteria included case files with incomplete records (five) and the only case resulting from orbital trauma.

Data were analyzed using Epi-info Version 6.04D (Centers for Disease Control and Prevention, Atlanta, GA, USA). P values less than 0.05 were considered statistically significant. This study adhered to the Tenets of the Declaration of Helsinki.

RESULTS

A total of 24 patients presented with cranial nerve palsies. There were 11 males and the male to female ratio was 1:1.2. The mean age of the patients was 34.50 ± 18.41 years (range, 4 years to 75 years). The age and gender distribution of the study subjects is as presented in Table 1. Most of the patients with cranial nerve palsies (N = 14/24; 58.3%) were between 20 years and 39 years old [Table 1].

Table 1

Age and gender distribution of patients with cranial nerve palsies

The most common presenting symptoms were headache and diplopia, affecting 7 (21.2%) patients each; this was followed by fever in 5 patients (15.2%) [Table 2].

Table 2

Presenting symptoms of patients with cranial nerve palsies

Visual acuity was normal (VA = 6/6) in 41 eyes (85.4%), impaired (VA <6/18) in 6.3% (N = 3) eyes and 4 eyes (8.3%) were blind (VA = <3/60). Table 3 presents the ocular findings. Two patients each (13.3%) had 15° exotropia and 15° esotropia, respectively, while two patients each (13.3%) had severe ptosis and complete ophthalmoplegia. Three patients (20.0%) had lagophthalmos and 8 of the 24 patients (33.3%) had sluggishly reactive pupils.

Table 3

Physical findings (ocular) of patients with cranial nerve palsies

Table 4 presents the type of cranial palsy. The 3rd and 6th cranial nerves were affected in seven patients each (29.2%; N = 7/24) while five patients (20.8%) had 7th cranial nerve palsy [Table 4]. Only four patients (16.6%) had multiple cranial nerve palsies [Table 4].

Table 4

Type of cranial nerve palsy in patients presenting to the University of Port Harcourt Teaching Hospital Eye Clinic

The relationship between cranial nerve palsy and pupillary reaction is presented in Table 5. Most cranial nerve palsies (70.8%; N = 17/24) were associated with normal pupillary reaction [Table 5]. Only 29.2% of cranial nerve palsies were associated with sluggishly reactive pupils. Those with 3rd and multiple cranial nerve palsies had sluggishly reactive pupils. The relationship between cranial nerve palsies and pupillary reaction was statistically significant (P = 0.02) [Table 5].

Table 5

Relationship between cranial nerve palsy and pupillary reaction

Table 6 presents the relationship between cranial nerve palsy and age. Most patients (48.3%; N = 11/24) with cranial nerve palsies were aged between 20 and 29 years old [Table 6]. This is followed by those in the 50-59 year age range, making up 16.7% (N = 4) of all cases of cranial nerve palsies [Table 6]. This relationship was statistically significant (P < 0.01) [Table 6].

Table 6

Relationship between cranial nerve palsy and age

Table 7 presents the relationship between cranial nerve palsy and systemic disorders. About 38% of those with cranial nerve palsies had systemic disorders. Of these, two (12.5%) were diabetic, four had systemic hypertension (16.7%) and one each had asthma, cerebral malarial and hearing loss [Table 7]. The relationship between cranial nerve palsy and systemic disorder was statistically significant (P < 0.01) [Table 7]. There was however no statistically significant difference between cranial nerve palsy and those with fever (not shown on table).

Table 7

Relationship between cranial nerve palsy and systemic disorder

DISCUSSION

Over a three-year period, only 24 cases of cranial nerve palsies presented, compared to other studies where larger numbers were seen. This is not surprising as stroke patients are rarely referred to our clinic from the medical outpatient department of the Hospital. The few patients who presented were “walk-ins” without referral. Similarly, some cases, especially facial nerves palsies are managed by the ENT department explaining the very small number reported here.

Our results show that most of the patients with cranial nerve palsies were between 20 and 39 years of age with a mean of 34.50 ± 18.41 years (range, 4-75 years). This differs from a study by Rowe et al.,4 where the mean age was 69.18 ± 14.19 years (range, 1-94 years). This difference is not surprising since Rowe et al.,4 study involved only stroke patients which may have accounted for the older age group as the risk factors to developing a stroke are greater in older individuals. The most common presenting symptoms were headaches, fever, diplopia and ptosis. Diplopia and ptosis are in keeping with the functions of some of the affected cranial nerves. The only patient with fever and neck stiffness had meningitis. Other fevers were ruled out as malaria as it is endemic in our region and commonly presents as fever.

In our study, most patients (87.5%) had horizontal diplopia. This was expected as the 3rd and 6th cranial nerves were the most affected. In a study of stroke patients, Rowe et al.,4 reported that the 3rd and 6th cranial nerves were most affected, similar to our study. Of the seven patients with 6th cranial nerve palsy, four were hypertensive, two were diabetic and one patient had cerebral malaria. This concurs with other studies where abducens palsy is considered the most commonly encountered extraocular muscle palsy with an incidence of 11.3 per 100,000 people.5 Berlit et al.,6 in their study of 165 patients suffering from abducens nerve palsy found that a vascular origin (29.7%) was the most common, followed by inflammatory diseases (19.4%) and tumors (10.9%), while traumatic abducens paresis (3.1%) was rare. This confirms an earlier report by Moster7 who identified vascular pathologies such as diabetes mellitus, hypertension and atherosclerosis. Moster found the vascular group was older compared to the younger group with multiple sclerosis and tumors as the more common causes.7

The mechanism of traumatic abducens nerve palsy may be direct mechanical injury or an indirect injury. The indirect injury results from nerve ischemic change due to vessel compression or vasospasm.89 The three cranial nerves (3rd, 4th and 6th) are fed by a comprehensive network of arterial blood vessels, and thus are susceptible to vascular compromise particularly localized lesions and disturbances at the level of the brainstem cranial nerve nuclei as well as in the cavernous sinus just before innervating the extraocular muscles.10

Paralysis of the 6th cranial nerve has no localizing value because it may be affected by, almost any type of cerebral lesion. Many theories have been proposed for this observation.11 Collier thought that this happens because of the shifting backwards of the brainstem since the direction of the nerve is mostly fronto-caudal. Affection of the 6th nerve is followed by the 3rd, 7th and 8th cranial nerves. The more fragile 4th nerve with its longer intracranial course (75 mm) is less affected because it is thought to be protected by, the free margin of the tentorium cerebelli. Alternately, the 6th nerve, has the longest extradural course (even though its entire length is 1/3 that of the 4th nerve), thereby making it vulnerable to intracranial insults as seen in meningitis and subarachnoid hemorrhage.12 Cushing13 postulated that when the anterior inferior cerebellar artery ran ventral to the 6th nerve it may press on and groove the nerve and the underlying pons due to increased intracranial pressure and thus cause lateral rectus palsy. Another author suggested that the bend over the sharp apex of the petrous temporal bone exposes the 6th nerve to insult when there is an increase in intracranial pressure with resultant coning of the brain. If the 6th nerve is fixed to the pons and more or less held in the cavernous sinus, it will therefore be pressed up against the sharp border of the petrous temporal bone causing an interruption in conduction and palsy of the lateral rectus. A similar condition may follow compression of the skull in difficult labor with or without forceps and may explain 6th nerve palsy at birth. A review of the medical literature1112 has shown that abducens nerve vulnerability results from factors other than its intracranial length.

Of the 24 patients we reviewed, only 9 underwent neuro-imaging. Eight results were normal and one showed an intracranial space-occupying lesion. The observation that the neuro-imaging results were normal should not give a false sense of hope. This was shown in a case reported by Hoenig14 of a 62-year-old male with facial nerve palsy who was managed over an 18-month period with initial normal magnetic resonance imaging results. Hoenig14 therefore cautioned that normal neuro-imaging results might be falsely misleading in identifying the cause of cranial nerve palsy.

In the current study, approximately one third (33.3%) of the patients had sluggishly reactive pupils; and the relationship between cranial nerve palsy and pupillary reaction was statistically significant (P = 0.02). Complete 3rd nerve palsy would almost definitely affect pupillary reaction, hence this result is not unexpected. All cases of 7th cranial nerve palsy were idiopathic except one patient who had associated hearing loss. Recent research has shown that Bell's palsy occurs when the herpes simplex virus gets reactivated in the temporal bone.15 This may explain the associated otalgia in one of the patients. Bell's palsy is the most common facial nerve palsy encountered, accounting for approximately 75% of cases.16

The limitations of this study included the very small sample size, and most patients were lost to follow-up. Hence it is difficult to assess the final outcome of management. A future study involving other departments that manage patients with cranial nerve palsies is required.

CONCLUSION

The most common cranial nerve palsies in patients present at the University of Port Harcourt Teaching Hospital Eye Clinic were the 3rd and 6th cranial nerves, followed by the 7th nerve. Most cases of 6th cranial nerve palsy were related to systemic disorders such as hypertension, DM and cerebral malaria. This association was statistically significant. A further study involving other relevant departments would provide a more comprehensive summary of the frequency of the occurrence of cranial nerve palsies.