Electromyography and nerve conduction studies in critical care: step by step in the right direction

Excerpt

Neuromuscular dysfunction is encountered in critical care, either as a primary cause of a patient’s admission to the intensive care unit (ICU) or as a complication of critical illness and its treatment. The scope of this paper is to introduce the readers to the concepts of critical illness polyneuropathy (CIP), critical illness myopathy (CIM) and intensive care acquired weakness (ICUAW), and provide an overview of the current diagnostic modalities and limitations. ICUAW is defined clinically utilizing the Medical Research Council (MRC) scale to assess strength in functional limb muscle groups when weakness cannot be explained by an alternative diagnosis [1]. CIP is a distal axonal sensory-motor polyneuropathy affecting peripheral nerves innervating limb and respiratory muscles and CIM a primary myopathy unrelated to muscle denervation [2]. The term critical illness polyneuropathy myopathy (CIPNM) is reserved for patients who have electrophysiological and/or histologic findings of coexisting CIP and CIM [2]. ICUAW, CIP and CIM are associated with worsened short- and long-term outcomes including difficulty weaning from mechanical ventilation, increased mortality and ICU and hospital length of stay, and long-term disability [3, 4]. A recent propensity-matched study found that multi-organ dysfunction, severe sepsis and hyperglycemia are associated with the development of CIP/CIM [5]. The diagnosis of neuromuscular disorders in the ICU relies on a combination of clinical, electrophysiological and morphological observations [2]. Deconditioning, wasting or disuse atrophy can occur due to any of these subtypes, but using electromyography (EMG)/nerve conduction studies (NCS) can help to identify the underlying cause for deconditioning. It is important to distinguish CIP from CIM as CIM has better short- and long-term prognosis than CIP [6]. The gold standard for diagnosing and distinguishing between CIPNM/CIM/CIP is skin and muscle biopsy. However, patients are usually not subjected to biopsies if the clinical and EMG/NCS are diagnostic of one of these subtypes. …