The first known case of myasthenic syndrome in association with lung cancer was published by Anderson et al (1) while Lambert et al (2) characterized the electrophysiologic pattern of this syndrome. Further research led to the discovery of the autoantibodies thought to be responsible for the characteristic clinical findings. Lambert–Eaton myasthenic syndrome (LEMS), which includes both paraneoplastic and autoimmune etiologies, commonly involves weakness of the proximal muscles, autonomic symptoms (e.g., decreased sweating and dry mouth), and reduced deep tendon reflexes. Involvement of the visual system is less well characterized. Ophthalmic symptoms, generally mentioned in other studies, have been reported with a prevalence ranging from 0% to 80% (3,4). The aim of our study was to further elucidate the ophthalmic symptoms and findings of LEMS.
The records of all patients with the diagnosis of LEMS from January 1, 1976, to December 31, 2010, were reviewed. Inclusion criteria were clinical features including reduced deep tendon reflexes, autonomic symptoms (dry mouth, constipation, impaired sweating, and impotence), and proximal muscle weakness. In addition, we required a diagnostic electromyography (EMG) (consisting of >10% decrement of compound muscle action potentials at 2 Hz stimulation and facilitation of >100% after brief exercise or 50 Hz stimulation) and/or the presence of voltage-gated calcium channel antibodies, N-type or P/Q-type. Historical information and examination findings were obtained from the medical record. Each patient's record was reviewed with special attention to ophthalmologic and neurologic examination findings. At a minimum, each patient had a neurologic examination, which included a basic eye examination including eyelid position, ocular motility, and pupillary testing.
The diagnosis of LEMS was mentioned in 241 records, and 176 met our inclusion criteria. Men represented 53.3% of the patients, and mean age at diagnosis was 60.3 years (range: 7–83 years). Malignancy was diagnosed either before diagnosis or during the follow-up period in 79 patients (44.9%), 65 of which were found to have small cell lung carcinoma.
Forty-two patients (24%) had an examination by an ophthalmologist at the time of presentation or during the follow-up period (up to 14.5 years). Twenty-five patients (14%) had onset of ophthalmic symptoms coincident with onset of systemic symptoms. Six patients (3%) had ophthalmic symptoms (3 with ptosis, 2 with diplopia, and 1 with decreased/blurred vision) before systemic symptoms. The most common ophthalmic complaints were ptosis and diplopia with 41 patients (23%) and 36 patients (20.5%), respectively. Less frequently, 24 patients (14%) reported decreased vision, and 12 patients had symptoms of dry eye.
Ophthalmic signs included ptosis in 45 patients (26%), which was asymmetric in 21 patients. Two patients each had fatigable ptosis and Cogan lid twitch. Motility dysfunction was noted in 15 cases (8.5%). Two patients had generalized decrease in motility, and 2 had eye movements described as dysconjugate. One patient was noted to have slow horizontal saccades, and 1 patient had findings of bilateral adduction weakness. Fourteen cases (8%) had some form of strabismus: esodeviation (4–18 prism diopters), exodeviation (4–10 prism diopters), and hyperdeviation (2–12 prism diopters). Additionally, 2 patients showed signs of convergence insufficiency.
Pupillary abnormalities were detected in 12 patients (7%), including 7 with sluggish pupils. Anisocoria was noted in 4. One patient was noted to have Horner syndrome, and another showed hypersensitivity to 0.125% pilocarpine.
Clinical signs of dry eye (staining with vital dyes or superficial punctate keratitis) were seen in 4 patients (2%).
Because of lack of standardized best-corrected visual acuity data, findings of blurred or decreased vision could not be accurately analyzed.
Two patients also were diagnosed with myasthenia gravis (MG). One of these patients had a positive edrophonium test before confirming the diagnosis of LEMS with an EMG. The second patient had acetylcholine receptor binding antibodies detected at the same time of LEMS diagnosis and subsequently had a positive edrophonium test.
Previous studies have shown that eyelid findings in LEMS are quite common with a range of 28%–54% of patients (5–7). Ptosis was the most common finding in our cohort and was generally mild. Brazis (8) identified enhanced ptosis in 1 patient with LEMS. Breen et al (9) reported a case of lid elevation on sustained upgaze and suggested that this may represent facilitation of the levator, similar to the facilitation seen in other muscle groups in LEMS. Cogan lid twitch seen in 2 of our patients is likely nonspecific (10,11).
Abnormalities in eye movements in our patients were generally mild and did not seem to have common pattern. Findings ranged from an isolated functional deficit to dysconjugate eye movements. Using quantitative oculography, Cruciger et al (12) and Dell'Osso et al (13) showed that facilitation can occur in extraocular muscles. Three studies (4–6) comprising 170 patients with LEMS documented ocular motility abnormalities in up to 30% of patients. Individual case reports are rare. Kanzato et al (14) described a 57-year-old man with bilateral ophthalmoparesis sparing abduction in both eyes. Rudnicki (15) reported a 52-year-old woman who noted diplopia on lateral gaze, but a clear description of her eye movements was lacking.
Diplopia as a symptom of LEMS has been reported in 21%–52% of patients (4,5,7,16–19). Objective signs of ocular misalignment have been reported to occur in 12%–50% in studies with 227 and 10 patients, respectively (4–7). Our data showed a lower prevalence with objective findings. Krieger and Goldchmit (20) reported 2 patients with isolated medial rectus weakness as the only ocular manifestation of LEMS. Both were successfully treated with strabismus surgery. None of our patients required strabismus surgery to treat their deviation.
Pupillary dysfunction in LEMS is an indicator of intraocular autonomic dysfunction. The most common sign of pupillary dysfunction in our study was sluggish pupils. O'Neill et al (5) reported that 6 of their 50 patients had sluggish pupillary light response, and 2 were noted to have postganglionic denervation hypersensitivity with response to dilute cholinergic agonists indicating parasympathetic dysfunction. The patient with LEMS described by Kanzato et al (14) exhibited Horner syndrome with hypersensitivity to alpha agonist drops demonstrating involvement of the sympathetic pupillary pathway. Clark et al (21) prospectively evaluated 13 eyes of patients with LEMS and found evidence of both sympathetic and parasympathetic denervation hypersensitivity in 4 of 7 patients, indicating generalized autonomic dysfunction. They additionally found abnormal pupil cycle time, a nonspecific indicator of pupillary reflex arc dysfunction, in 9 of 13 eyes.
Another ocular indicator of autonomic function is ocular surface lubrication. Dry eye is difficult to quantify as some patients exhibiting subjective symptoms have no objective findings on clinical examination. Previous studies indicate that between 4% and 29% of patients complain of symptoms of dry eye (7,17,19). Clark et al (21) prospectively tested the reflex tear production in 7 patients with LEMS (13 eyes) and found that 9 eyes had abnormal results.
LEMS and MG may occur in the same patient, and there can be considerable overlap in the clinical eye findings (22–25). The distribution of muscle weakness in LEMS is certainly different from MG; in MG, weakness develops in a craniocaudal direction and in the opposite direction in LEMS (3). Although extraocular motor symptoms are more common in MG, autonomic symptoms (specifically pupillary involvement and dry eye) are not a part of the MG symptom complex (26).
Our study is limited by its retrospective nature, and most of the patients were examined by a specialist in neurology and not ophthalmology. As a tertiary medical center, the studied patient population may have been biased. Follow-up was also limited.
This is the largest single-institution series of patients with LEMS and to the best of our knowledge, the only large series focusing on ophthalmic symptoms and findings. Patients with LEMS may present with ophthalmic symptoms as part of the initial symptom complex and can very rarely manifest with ophthalmic symptoms before the onset of systemic symptoms (15,27). Titulaer et al (17) showed that ophthalmic findings occur soon after the diagnosis but not necessarily as soon as other symptoms such as proximal weakness. Some of our patients had been followed elsewhere before definitive diagnosis at our institution, resulting in their presentation later in the clinical course. Therefore, we could not further define ocular manifestations based on the chronicity of the disease.
STATEMENT OF AUTHORSHIP
Category 1: a. Conception and design: J. D. Young and J. A. Leavitt; b. Acquisition of data: J. D. Young; c. Analysis and interpretation of data: J. D. Young. Category 2: a. Drafting the article: J. D. Young; b. Revising it for intellectual content: J. D. Young and J. A. Leavitt. Category 3: a. Final approval of the completed article: J. D. Young and J. A. Leavitt.
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