Myasthenia gravis, a disease of the neuromuscular junction, can be accompanied by respiratory difficulties (dyspnoea, congestion, ineffective cough …) whose occurrence over a few days, associated with a rapid motor deterioration, leads to the diagnosis myasthenic crisis. This exacerbation of the disease constitutes a vital emergency, which requires hospitalization in intensive care.
An easy and useful evaluation
Single-breath count test (SBCT) can be useful in this context. Much simpler than the functional respiratory tests, it consists in making the patient count out loud after maximum inspiration. The result corresponds to the number reached with a normal voice, without having to take a breath. It is correlated with vital capacity in myasthenia gravis, as demonstrated in 2016. A new study, carried out by an American team, evaluated the SBC test carried out by telephone by a nurse trained in its use in 25 patients with generalized myasthenia gravis. Over a period of one year, they made 45 calls to their expert center to report symptoms suggestive of a myasthenic crisis:
- a SBC test result below or equal to 25 had a positive predictive value of 71%, a sensitivity of 80% and a specificity of 60% to diagnose a myasthenic crisis;
- all the patients who could not count above 22 had an exacerbation of their disease, and none of the patients able to count above 28 had it;
- the most specific symptoms to predict an attack were in this study diplopia, dysphagia and ptosis.
