Respiratory Assessment of Myasthenia Gravis Patients Using Repetitive Nerve Stimulation of Phrenic and Intercostal Nerves.

BACKGROUND

We evaluated decremental response from phrenic and intercostal nerves using slow repetitive nerve stimulation test (RNST) to look for its diagnostic significance in sero-negative predominantly bulbar myasthenia gravis (MG) with normal peripheral or cranial nerve RNST.

METHODS

RNST from phrenic and intercostal nerves was performed along with standard RNST from abductor digiti minimi (ADM), trapezius, nasalis and orbicularis oculi muscles in 10 normal individuals (group I), 10 patients with neurological disorders other than MG (group II) and 10 patients with MG (group III). We evaluated the presence of positive response in first two groups (group I and II) and absence of negative response in group III. Spirometry was also performed in MG patients.

RESULTS

Mean baseline decrement in I/C RNST in three groups was -2.06±1.33 %, -2.5±2.18% and -27.1±17.9 % respectively. One minute post exercise decrement in I/C RNST in three groups was -2.9±1.36%,-2.9±1.36% and -32.9±17.9% respectively. RNST of phrenic nerve showed mean baseline decrement of -2.1±2.3%, -3.2±2.6 % and -18.3±30.3% in three groups respectively. One minute post exercise decrement percentage were -2.2±1.18% in group I, -4.8±2.18% in group II and -29.2±19.2% in group III. RNST of peripheral nerves were negative in two patients who were bulbar sero-negative MG, however, significant decrement was seen in intercostal and phrenic nerve RNST.

CONCLUSION

Intercostal and phrenic nerve RNST are a better test for assessing respiratory involvement specially in patients presenting with bulbar symptoms and having negative RNST of peripheral nerves.