REPETITIVE PHRENIC NERVE STIMULATION: USEFULNESS IN DIAGNOSTIC WORK‐UP OF MIASTENIA GRAVIS (MG)

Cocito D., Isoardo G., Ciaramitaro P., Proto G., Testa M., Durelli L., Bergamasco B. Dipartimento di Neuroscienze, Università di Torino OBJECT : To evaluate sensitivity and specificity of repetitive nerve stimulation on diaphragm muscle stimulating phrenic nerve (RNS‐DIAP) for diagnosis of MG, in comparison with RNS on abductor digiti minimi stimulating ulnar nerve (RNS‐ADM) and on deltoid muscle stimulating axillary nerve (RNS‐DELT). PATIENTS AND METHODS : We performed RNS‐DIAP, RNS‐DELT and RNS‐ADM in 12 MG patients (9 women, 3 men, mean age: 55 ± 19 years) and 12 healthy controls (4 women, 8 men, mean age: 33 ± 14). RESULTS : Only 2 of 12 MG patients had positive RNS‐ADM (‐10% change in M‐response area at fifth response), 11 had positive RNS‐DELT and 12 had positive RNS‐DIAP. Mean decrease in CMAP area was 8 ± 9% in RNS‐ADM, 27 ± 13% in RNS‐DELT and 31 ± 10% in RNS‐DIAP. Difference between decrease in CMAP area was significant only between RNS‐DIAP and RNS‐ADM (p=0.002) and between RNS‐DELT and RNS‐ADM (p=0.0003). There was a weak correlation between clinical MG score and decrease in CMAP area in RNS‐DIAP, however, 3 of 12 positive patients developed respiratory failure a few days after the test. DISCUSSION : In our hands, RNS‐DIAP has no significant advantage as compared to RNSW‐DELT in terms of sensitivity and specificity for MG diagnosis. Furthermore, this test was not well tolerated by the vast majority of patients.