Ocular myasthenia gravis and risk factors for developing a secondary generalisation: Description of a Spanish series

INTRODUCTION

Ocular myasthenia gravis (MG) is the most common phenotype of MG at onset. A variable percentage of these patients develop secondary generalisation; the risk factors for conversion and the protective effect of immunosuppressive treatment are currently controversial.

PATIENTS AND METHODS

We designed a retrospective single-centre study with the aim of describing the demographic, clinical, and laboratory characteristics of a Spanish cohort of patients with ocular MG from Hospital Universitario de Albacete from January 2008 to February 2020.

RESULTS

We selected 62 patients with ocular MG from a cohort of 91 patients with MG (68.1%). Median age at diagnosis was 68 (IQR, 52-75.3), and men accounted for 61.3% of the sample (n = 38). Most patients presented very late-onset ocular MG (n = 34, 54.8%). Binocular diplopia was the most frequent initial symptom (51.7%). The rate of progression to generalised MG was 50% (n = 31), with a median time of 6 months (IQR, 2-12.8). Female sex (OR: 5.46; 95% CI, 1.16-25-74; p = .03) and anti-acetylcholine receptor antibodies (OR: 8.86; 95% CI, 1.15-68.41; p = .04) were significantly associated with the risk of developing generalised MG.

CONCLUSIONS

The conversion rate observed in our series is relatively high. Generalisation of MG mainly occurs during the first 2 years of progression, and is strongly associated with female sex and especially with the presence of anti-acetylcholine receptor antibodies.

Antibody profile may predict outcome in ocular myasthenia gravis

An unsolved issue remains whether there are clinical and immunological features to predict in a single patient the risk of conversion from ocular Myasthenia Gravis (OMG) to generalized disease (GMG) as 50-60% of patients may progress within 1-2 years since onset. Anti-acetylcholine receptor antibodies (AChR Abs) are found in up to 50% of OMG patients; muscle-specific tyrosine kinase antibodies (MuSK-Abs) are present in about 70% of the whole seronegative (SN), who usually develop a severe disease with bulbar involvement. We surveyed a cohort of 175 OMG patients with purely ocular symptoms and we compare the outcome of patients with antibodies to AChR or to MuSK with those seronegative for both Abs (DSN). All patients had purely ocular signs for at least 24 months. Gender, age at onset, time to generalization or to worsening in quantitative ocular QMG scores, electrophysiological results were analyzed. Males were 58.9%, females 41.1%. Patients with late onset of symptoms after 50 years (LOMG) were 78.3%. We assayed anti-MuSK-Abs in 4.7%, anti-AChR Abs in 38.5%; 57.3% were defined DSN. Thirty-seven patients (21.1%) progressed to GMG during the observational time: 23 were females, 62% of the whole group of the generalized subjects, 75% of MuSK-positive OMG converted to GMG versus the 26.2% of AChR positive and 13.7% of DSN. Statistical analysis showed that gender and presence of antibodies either to AChR or to MuSK were independent predictors of worse outcome; the DSN subjects had lower risk of conversion to GMG.