Sixth Nerve Palsy
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COMPREHENSIVE OPHTHALMOLOGY UPDATE VOLUME 7, NUMBER 5 SEPTEMBER-OCTOBER 2006 CLINICAL PRACTICE Sixth Nerve Palsy THOMAS J. O’DONNELL, MD, AND EDWARD G. BUCKLEY, MD Abstract. The diagnosis and etiologies of sixth cranial nerve palsies are reviewed along with non- surgical and surgical treatment approaches. Surgical options depend on the function of the paretic muscle, the field of greatest symptoms, and the likelihood of inducing diplopia in additional fields by a given procedure. (Comp Ophthalmol Update 7: xx-xx, 2006) Key words. botulinum toxin (Botox®) • etiology • sixth nerve palsy (paresis) Introduction of the cases, the patients had hypertension and/or, less frequently, Sixth cranial nerve (abducens) palsy diabetes; 26% were undetermined, is a common cause of acquired 5% had a neoplasm, and 2% had an horizontal diplopia. Signs pointing aneurysm. It was noted that patients toward the diagnosis are an who had an aneurysm or neoplasm abduction deficit and an esotropia had additional neurologic signs or increasing with gaze toward the side symptoms or were known to have a of the deficit (Figure 1). The diplopia cancer.2 is typically worse at distance. Measurements are made with the Anatomical Considerations uninvolved eye fixing (primary deviation), and will be larger with the The sixth cranial nerve nuclei are involved eye fixing (secondary located in the lower pons beneath the deviation). A small vertical deficit may fourth ventricle. The nerve on each accompany a sixth nerve palsy, but a side exits from the ventral surface of deviation over 4 prism diopters the pons. It passes from the posterior Dr. O’Donnell is affiliated with the should raise the question of cranial fossa to the middle cranial University of Tennessee Health Sci- additional pathology, such as a fourth fossa, ascends the clivus, and passes ence Center, Memphis, TN. Dr. cranial nerve palsy or skew under the petro-clinoid ligament in Buckley is affiliated with the Duke deviation.1 Dorello’s canal. It then enters the University Eye Center, Durham, NC. In a recent population-based study cavernous sinus where, unlike its that reviewed 137 patients spanning fellow cranial nerves, it is Reprint address: Edward G. Buckley, a 15-year period, the sex incidence unsupported by the dural wall of the MD, Duke University Eye Center, was equal, the annual incidence was sinus. It passes through the superior Box 3802, Durham, NC 27710 11.3/100,000, and the peak incidence orbital fissure and into the orbit email: [email protected] was in the seventh decade. In 35% through the annular ligament of the © 2006 by Comprehensive Ophthalmology Update, LLC. All rights reserved. 1 2 Comp Ophthalmol Update 7 (5) September-October 2006 O’DONNELL Fig. 1. Patient with a microvascular right sixth nerve palsy. Note the lack of abduction of the right eye. Fig. 2. Patient with a right carotid artery aneurysm in the cavernous sinus causing a right sixth nerve palsy with a right Horner syndrome. Note the lack of abduction of the right eye, miosis, and ptosis. rectus muscles, and then to the lateral additional neurologic or ocular signs) found a strong association with both rectus. is a common presentation (Table 2). diabetes and coexistent diabetes and Although shorter in length than the Traditionally, adults over 50 years of hypertension, but not with fourth cranial nerve, the course of age presenting with isolated sixth hypertension alone.8 Scott reviewed the sixth nerve leaves it vulnerable to nerve palsy and with vasculopathic the long-term outcome of 59 a variety of insults.3 Lesions in the risk factors (diabetes, hypertension) patients with vasculopathic sixth pons may be associated with may be observed without imaging nerve palsy and reported that 86% internuclear ophthalmoplegia, for 3 months, as a microvascular had complete resolution of the palsy, ipsilateral horizontal gaze palsy, and etiology is common. Warwar recently and that five of eight patients with contralateral long tract signs presented a case of a 68-year-old incomplete resolution were (weakness), as well as the possible man with vasculopathic risks who asymptomatic. He cautioned, involvement of cranial nerves V, VII, presented with an isolated sixth nerve however, that almost one-third of and VIII (Table 1). After exiting the palsy secondary to pituitary apoplexy.6 these patients had at least one pons, the nerve is susceptible to The patient developed a third cranial recurrent episode.9 An MRI should increases in intracranial pressure from nerve palsy a few days after be performed in younger adults with a variety of causes. Petrous bone presentation, went into cardiac arrest, isolated sixth nerve palsy, and in all trauma or inflammation may be and died. The author recommended patients with sixth nerve palsy associated with decreased hearing, that neuroimaging be considered in accompanied by additional cranial facial pain, numbness, or patients with isolated sixth nerve nerve or other neurologic findings. hemotympanum. Cavernous sinus palsy, even in the presence of a strong The studies by Warwar and Bendszus lesions or superior orbital fissure vasculopathic history. raise controversy about whether to lesions are highlighted by fellow A prospective study of 43 patients image all patients with acute sixth cranial nerve palsies or Horner (ages 2–82, mean age = 48) with nerve palsy. syndrome (Figure 2). A sixth nerve isolated sixth nerve palsies by Patients with bilateral or nonisolated palsy with proptosis and conjunctival Bendszus identified 63% with lesions sixth nerve palsy should have an inflammation points toward an considered relevant to the palsy on MRI, medical work-up, and lumbar orbital process.4,5 MRI.7 Of these patients, 49% had puncture. Accompanying neurologic tumor or tumor-like lesions. Repeat deficits may point toward areas of Clinical Considerations MRI at 3–6 months was normal in the brain to focus on as discussed all patients with initial normal MRIs. above. Infectious etiologies, such as An isolated sixth nerve palsy (no The authors recommended MRI in botulism or cytomegalovirus (CMV), all patients presenting with acute sixth neoplasm (nasopharyngeal cancer), or nerve palsy, even with a inflammatory causes, such as Focus Point #1 vasculopathic history. Guillain-Barre syndrome, should be Patel, in a study of 76 patients with kept in mind.10 An esotropia increasing to one side may indicate a subtle sixth isolated nontraumatic sixth nerve Pain with a sixth nerve palsy is nerve palsy. palsy without a suspected systemic nonspecific. A microvascular sixth etiology other than microvascular, nerve palsy may or may not be SIXTH NERVE PALSY 3 Table 1 Table 2 Location and Signs of Cranial Nerve Six Lesions Etiology of Cranial Six Nerve Lesions Site of Lesion Affecting Cranial Nerve VI Possible Associated Signs/Symptoms Adult Pons/brainstem Horizontal gaze palsy Microvascular: age 50, vasculopathic risks Internuclear ophthalmoplegia Trauma Involvement of cranial nerves V, VII, Neoplasm VIII Infection (meningitis) Contralateral weakness Inflammation Nystagmus Increased intracranial pressure Aneurysm Cerebello-pontine angle Involvement of cranial nerves VII, VIII Pituitary apoplexy Cerebellar signs, nystagmus Idiopathic Subarachnoid course Signs of increased intracranial Child pressure Postviral illness Petrous bone Involvement of cranial nerves V, VII, Trauma VIII Neoplasm Ear infections, mastoiditis Infection (meningitis) Inflammation Cavernous sinus/superior orbital fissure Involvement of cranial nerves III, IV, Increased intracranial pressure V(1) or sympathetics to pupi (i.e., Congenital (Duane, Mobius) Horner syndrome) Aneurysm Idiopathic Orbit Proptosis Conjunctival inflammation, chemosis accompanied by pain. An etiology of sixth nerve palsy in 75 frequent cause of sixth nerve palsies inflammatory etiology, such as children.11 In contrast, Holmes, in a in children (Tables 2 and 3). Tolosa-Hunt syndrome, is painful population-based study of cranial and typically responds quickly to nerve palsies in children, found no Differential Diagnosis steroids. Other etiologic cases of neoplasia with isolated considerations would include palsies.12 An abduction deficit may be aneurysm, bone metastasis, and A sixth nerve palsy secondary to secondary to poor function due to ophthalmoplegic migraine. chronic middle ear infections and cranial nerve palsy, mechanical A child may develop a sixth nerve mastoiditis is less commonly seen restriction, a disease process affecting palsy following a viral illness, and the with current antibiotics and muscular function, or a congenital role of MRI in children with isolated immunizations. Pseudotumor cerebri disorder (Table 4). Restriction of the sixth nerve palsy is controversial. can be seen in children, and may be medial rectus may be the direct result Neuroimaging is recommended in a accompanied by a sixth nerve palsy. of medial orbital wall trauma, and a child with persistent, bilateral, or sixth Duane and Mobius syndromes have “tight” medial rectus may occur with nerve palsy accompanied by other abduction defects, but the deficits are time with any palsy of the lateral neurologic signs or symptoms. At a associated with other signs (palpebral rectus. Thyroid eye disease and tertiary referral center, Lee found fissure narrowing in the former, orbital inflammatory disease may neoplasm or neoplasm-related facial paresis in the latter). Trauma, result in restriction of extraocular surgery to be the most common unfortunately, continues to be a muscles, but are typically Fig. 3.