PM&R News   •   February 2018

Research continues to be performed looking into the causes and treatments of critical illness polyneuropathy (CIP) and critical illness myopathy (CIM). It was not long ago that we thought these two diagnoses were independent of each other. Now we are finding out they often occur together and can be found in up to 50% of severely critical ill patients. With this research, new studies have shown screening electrodiagnostic studies to best assist in diagnosing these entities. To review, critical illness polyneuropathy usually shows a sensory-motor axonal polyneuropathy and clinically the patient can have difficulty weaning from the ventilator, have a loss of deep tendon reflexes, and other lower motor neuron signs. The electromyographer usually appreciates low amplitudes of both compound motor action potential (CMAP) and sensory nerve action potential (SNAP), with latency and conduction velocity remaining normal to slightly reduced. Critical illness myopathy will also have associated myopathic motor units and early recruitment. Latronico et al looked at patients with ICU stays >3days and performed standard NCS/EMG testing as well as peroneal nerve test (PENT) by two independent board certified technicians. PENT testing consisted of testing the peroneal nerve to extensor digitorum brevis CMAP in one leg and if normal then testing in the other leg. If both were normal, then the test was considered negative and the test was abnormal if the CMAP was reduced below normal in at least one leg. Standard NCS/Emg consisted of ulnar motor to abductor digiti minimi bilaterally, peroneal motor to extensor digitorum brevis bilaterally, tibial motor to abductor hallucis bilaterally, F response of ulnar and tibial nerve, ulnar sensory to the little finger bilaterally, and sural sensory bilaterally, followed by needle emg. Standard NCS/EMG has a sensitivity of 90% and a specificity of 65% which this study set out to improve upon. Latronico et al investigated 121 patients and found that PENT had a sensitivity of 100% and a specificity of 85.2%. In addition the time to perform the study decreased by 40 minutes and patient discomfort was extremely minimized. PENT testing did demonstrate 4 false positives that ended up being peroneal mononeuropathy due to the criteria of having one abnormal peroneal nerve CMAP. Further studies could be beneficial to determine if specificity can be increased by potentially performing two nerve CMAPs regardless if the first is positive. We hope this study gives you something to think about as you next approach an inpatient study for CIP/CIM.