Long-term follow-up of strabismus surgery for patients with ocular myasthenia gravis

[Ocular myasthenia gravis]

Myasthenia gravis is an autoimmune disease characterized by muscle weakness and pathological fatigue due to autoaggressive phenomena with the formation of antibodies directed against various structures of the neuromuscular synapse. In most patients, the disease begins with the involvement of extraocular muscles, presenting with symptoms such as intermittent ptosis of the upper eyelid and/or binocular diplopia. In 15% of cases, clinical manifestations are limited to impairment of the levator palpebrae superioris and extraocular muscles, characteristic of the ocular form of myasthenia gravis. Specialists often encounter challenges in diagnosing this form, as serological and electrophysiological studies may be uninformative, necessitating diagnosis based on patient history and clinical picture. This literature review outlines the key aspects of the pathogenesis, clinical manifestations, methods of diagnosis and treatment of ocular myasthenia gravis.

Importance of clinical tests in ocular myasthenia

A 24-year-old otherwise healthy male presented to us with unilateral ptosis and contralateral lid retraction with limitation of extraocular movements; the disease had a gradual chronic course, which raised a suspicion of ocular myasthenia. Ice pack test was performed, which improved the ptosis; further investigations confirmed the diagnosis of ocular myasthenia. Patient was started on pyridostigmine and oral prednisolone which improved the extraocular movements and ptosis.

Don't Miss This! Red Flags in the Pediatric Eye Examination: Ophthalmoplegia in Childhood

Paralytic strabismus in children is rare, occurring in about 0.1% of children. This rate is far less common than the 3% rate usually noted for comitant strabismus. The relative rates of ocular motor pareses were fourth nerve palsies in 36%, sixth in 33%, third in 22%, with multiple ocular motor nerve palsies in 9%. In a single population series from Minnesota, few cases were associated with neoplasm. However, institutional case series reports a high rate of neoplasm for acquired third nerve and sixth nerve palsies after excluding trauma and congenital causes. Tumor is rare in children with fourth cranial nerve palsies, usually associated with other neurologic disease. Rare causes of external ophthalmoplegia, to be considered when the motility pattern is variable or not fitting an ocular motor nerve pattern, include myasthenia gravis and congenital fibrosis of the extraocular muscles. Myasthenia most often presents as ptosis with exotropia. Rarer still is involvement of the extraocular muscles in childhood thyroid disease.

Causes and surgical treatment of diplopia and strabismus secondary to myasthenia gravis

OBJECTIVE

To present a report of the ocular motility disorders, treatment and outcomes of myasthenia gravis (MG).

MATERIAL AND METHOD

A retrospective study was performed on the data of patients with MG. An evaluation was made using mean age, gender, initial diagnosis, ocular deviation, time of onset of clinical characteristics, treatment and results. Resolution of diplopia and/or ocular deviation in primary and reading gaze was considered a good outcome at the end of follow-up.

RESULTS

A total of 14 cases were included. The mean age of the sample was 55.64 years, of which 9 were women, and 10 cases were bilateral. The diagnosis was made by ophthalmologists in 4 cases. The initial diagnoses were diverse: bilateral cranial third nerve palsy in 3, unilateral third nerve palsy in 1, superior or inferior rectus palsy in 3, sixth nerve palsy in 2, fourth nerve palsy in 1, exotropia in 3 and esotropia in 1. Diplopia was presented in 14 cases and 9 associated ptosis. The different types of strabismus were horizontal ocular deviation in 11 cases: 8 with exotropia, and 4 with vertical deviation. Strabismus surgery was performed in 4 cases that did not respond to medical treatment, with a good final outcome. Pharmacological treatment resolved diplopia in 6 cases, and prisms in one. Ptosis surgery was only necessary in one patient. Outcome was favourable in 78.57% at the end of follow-up.

CONCLUSION

Acute onset diplopia caused by strabismus with variable angle or oculomotor palsy, associated or not with a ptosis can indicate MG. There were favourable outcomes with strabismus surgery. Pharmacological treatment did not resolve the diplopia in all cases.

Treatment of Ocular Myasthenia Gravis

Myasthenia gravis is a relatively common neuromuscular disorder, with ocular myasthenia gravis being a subset defined as myasthenia gravis limited to the orbicularis, levator, and extraocular muscles. Patients with ocular myasthenia gravis can have disabling diplopia or functional blindness from ptosis and in most cases treatment is required. Like generalized myasthenia gravis, there are a variety of treatments available that include pyridostigmine, immunosuppression, intravenous immunoglobulin, plasmapheresis, thymectomy, lid crutches, ptosis surgery, and extraocular muscle surgery. Unfortunately, there is limited data on the use of individual treatments in ocular myasthenia gravis and no data comparing treatments. Using a combination of available data on treatment of generalized myasthenia gravis, data on treatment of ocular myasthenia gravis, best practices, and clinical experience we will provide a rational framework for treatment of ocular myasthenia gravis.

Update on ocular myasthenia gravis in Taiwan

Myasthenia gravis (MG) is an autoimmune disease involving the neuromuscular junction. Autoantibodies to the acetylcholine receptor or, less frequently, to muscle-specific kinase, attack against the postsynaptic junctional proteins, resulting in fluctuating and variable weakness of muscles. Extraocular, levator palpebrae superioris, and orbicularis oculi muscles are particularly susceptible. The majority of patients with MG present with purely ocular symptoms including ptosis and diplopia initially. About half of these patients progress to generalized disease within 2 years. The prevalence of MG in Taiwan is 140 per million with male to female ratio of 0.7. The incidence rate is higher in the elderly. Several immune-related diseases such as lymphoid malignancy, diabetes, and thyroid diseases are associated with MG in the national population-based studies in Taiwan. Ice pack test, rest test, Tensilon/neostigmine test, circulating antibody measurement, and electrophysiological studies are useful diagnostic tools with variable sensitivity and specificity. For the patients with ocular MG, acetylcholinesterase inhibitors are usually the first-line treatment. Corticosteroids and immunosuppressant could provide better disease control and may reduce the risk of conversion to generalized form although there is still some controversy. A thymectomy is also beneficial for ocular MG, especially in refractory cases. The correction of ptosis and strabismus surgery could improve the visual outcome but should be performed only in stable disease.

Pediatric Myasthenia Gravis

Myasthenia gravis is a disorder of neuromuscular transmission that leads to fatigue of skeletal muscles and fluctuating weakness. Myasthenia that affects children can be classified into the following 3 forms: transient neonatal myasthenia, congenital myasthenic syndromes, and juvenile myasthenia gravis (JMG). JMG is an autoimmune disorder that has a tendency to affect the extraocular muscles, but can also affect all skeletal muscles leading to generalized weakness and fatigability. Respiratory muscles may be involved leading to respiratory failure requiring ventilator support. Diagnosis should be suspected clinically, and confirmatory diagnostic testing be performed, including serum acetylcholine receptor antibodies, repetitive nerve stimulation, and electromyography. Treatment for JMG includes acetylcholinesterase inhibitors, immunosuppressive medications, plasma exchange, intravenous immunoglobulins, and thymectomy. Children with myasthenia gravis require monitoring by a pediatric ophthalmologist for the development of amblyopia from ptosis or strabismus.

Isolated schwannoma involving extraocular muscles

BACKGROUND

Progressive strabismus initially considered idiopathic may be caused by isolated schwannomas of motor nerves to extraocular muscles, detectable only on careful imaging. This study reviewed clinical experience of a referral practice in identifying schwannomas on magnetic resonance imaging (MRI).

METHODS

We reviewed 647 cases imaged for strabismus to identify presumed cranial nerve schwannomas, identified by gadodiamide-enhanced, high-resolution surface coil orbital MRI and thin-section cranial MRI. Clinical features and management were correlated with MRI.

RESULTS

Schwannomas were identified as fusiform intraneural enlargements in 8 cases: 1 affecting the trochlear nerve; 2, the abducens nerve; and 5 the oculomotor nerve. Involved muscles were atrophic. Both abducens schwannomas, 1 superior oblique, and 1 oculomotor schwannoma were subarachnoid; 3 were intraorbital, and bilateral oculomotor lesions of 1 case extended from cavernous sinus to orbit. Associated strabismus progressed for 3-17 years. Abducens schwannoma caused esotropia; trochlear schwannoma caused hypertropia and cyclotropia. Intracranial oculomotor schwannoma caused mydriasis and exotropia. Intraorbital schwannoma caused exotropia with or without hypertropia. Since lesion diameters were 3-9 mm, 6 had been previously missed on routine MRI.

CONCLUSIONS

Progressive, acquired strabismus may be caused by isolated cranial nerve schwannomas, representing about 1% of strabismus cases in this study, involving the oculomotor more than abducens nerve. Because most schwannomas are small and deep in the orbit, findings could be readily missed by routine imaging, leading to a possible diagnosis of idiopathic strabismus. Schwannomas should be suspected when extraocular muscles are atrophic, but the causative lesions themselves are identifiable only using targeted, high resolution MRI.

Functional and Motor Outcomes of Strabismus Surgery for Chronic Isolated Adult Sixth Nerve Palsy

Abducens nerve palsy is the most common acquired ocular motor nerve palsy in adults. Chronic cases of abducens palsy often require surgical intervention to relieve disabling diplopia. The goal of this study was to identify factors associated with surgical outcomes in isolated abducens palsy. Medical records of all adult patients from 1988 to 2012 with abducens palsies who underwent strabismus procedures were retrospectively reviewed. Motor alignment, extraocular motility, and sensory outcomes were recorded. Success was defined as absence of diplopia without prisms or face turn, vertical deviation ≤2 prism dioptres (PD), and horizontal deviation ≤10 PD. Eighty-one patients (age range: 20-86 years) met inclusion criteria. Success was achieved in 58% of patients. Final success rates for abducens palsy were 50% for neoplastic, 59% traumatic, 57% for microvascular/unknown, and 67% for other central nervous system causes (p > 0.05). Patients with an underlying neoplastic or traumatic aetiology required more than one strabismus procedure more often than those with microvascular/idiopathic or other central nervous system causes (48% vs. 24%; p = 0.03). For complete abducens palsies, patients who underwent Hummelsheim-type procedures had a higher success rate than those who underwent a full-tendon vertical rectus muscle transposition. (78% versus 35%; p = 0.049). Success rates for strabismus procedures in patients with abducens palsies are similar across all aetiologies. Frequency of re-operation is higher among those patients with neoplastic or traumatic aetiologies for their abducens palsies. Hummelsheim-type procedures have a higher success rate for complete abducens palsies than full-tendon vertical rectus transpositions.