Laird Harrison

February 26, 2015

CORONADO, California — A new scoring system has identified three predictors of the risk for conversion from ocular myasthenia gravis to the generalized form of the disease.

"It could potentially be used in patient counseling," investigator Sui Wong, MBBS, from Moorfields Eye Hospital in London, United Kingdom, told Medscape Medical News.

Dr Wong presented the findings here at the North American Neuro-Ophthalmology Society 2015 Annual Meeting.

Myasthenia gravis typically presents as ocular disease. It is estimated that the risk for conversion to the generalized form of the disease ranges from 30% to 80%. Currently, there is no test to determine which cases will convert.

Most studies of risk factors are flawed because they include patients on immunosuppression, Dr Wong explained.

To find a way to accurately assess risk, Dr Wong and her colleagues retrospectively reviewed the medical records of 101 adults. All had ocular myasthenia for at least 3 months, and had not received immunosuppressive therapy for at least 2 years or before the onset of generalized myasthenia gravis.

In the 2 years after presentation with ocular disease, 19 patients developed generalized myasthenia; another 12 converted after that.

On statistical analysis, three predictors of conversion were identified: seropositivity, the presence of one or more comorbidities, and thymic hyperplasia. Age, sex, and autoimmunity status were not risk factors for progression.

Table. Predictors of Conversion

Predictor Positive (n/N) Equivocal (n/N) Negative (n/N) P Value
Seropositivity 14/43 2/10 3/48 <.01
Comorbidities 18/73 1/28 <.01
Thymic hyperplasia 2/3 17/83 .09

 

From this analysis, Dr Wong's team developed a scoring system that assigned 1 point to each predictor. Patients with a score of 1 or 0 were considered low risk, and those with a score of 2 or higher were considered high risk. They then calculated the probability of converting to be 7% for low-risk patients and 39% for high-risk patients.

The scoring system had a negative predictive value of 91%, a positive predictive value of 38%, a sensitivity of 79%, a specificity of 63%, and an area under the receiver operating characteristic curve of 0.74.

This is the first time anyone has shown thymic hyperplasia or the presence of comorbidities to be a risk factor, Dr Wong reported.

However, she cautioned, this is a proof-of-principle retrospective study that needs to be validated in a prospective study.

She explained that the scoring system could be used to design a randomized controlled trial in which patients at high risk of converting could be given corticosteroids and others could be given placebo. Because the risk for adverse reactions with corticosteroids is high, clinicians would like to know which patients are most likely to benefit from them.

In the discussion that followed Dr Wong's presentation, a member of the audience asked what comorbidities were included in the analysis.

Dr Wong explained that the researchers simply distinguished between perfectly healthy patients and those with anything in their medical records.

"We have to study this further," she acknowledged, "but we can't get away from the fact that this was highly statistically significant."

Such a vague description of comorbidities could be a flaw in the scoring system, said session moderator Matthew Thurtell, MBBS, from the University of Iowa in Iowa City.

"I think that the algorithm needs a little refinement before it's really ready for prime time," Dr Thurtell told Medscape Medical News.

Dr Wong and Dr Thurtell have disclosed no relevant financial relationships.

North American Neuro-Ophthalmology Society (NANOS) 2015 Annual Meeting. Presented February 24, 2015.

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