Update in Nonpulmonary Critical Care Acquired Neuromuscular Disorders in the Intensive Care Unit

Neuromuscular abnormalities developing as a consequence of critical illness can be found in the majority of patients hospitalized in the intensive care unit (ICU) for 1 week or more (1–3). The spectrum of illness ranges from isolated nerve entrapment with focal pain or weakness, to disuse muscle atrophy with mild weakness, to severe myopathy or neuropathy with associated severe, prolonged weakness. This update focuses on disorders associated with diffuse, severe weakness. The prevalence and impact of acquired neuromuscular weakness is likely larger than generally recognized. Greater than 50% of patients mechanically ventilated for more than 7 days will develop electrophysiologic abnormalities (4), with 25–33% developing clinically overt weakness (5, 6). Acquired neuromuscular dysfunction is associated with difficulty in separating from mechanical ventilation, increased hospital costs, and increased mortality (3, 7). The potential economic impact of this problem is large, with one estimate of an average of $66,000.00 per patient in excess hospital charges attributable to acquired neuromuscular weakness in the ICU (1996 U.S. dollars) (8). A clear classification of ICU-acquired neuromuscular disorders is difficult because of inconsistencies in reporting, testing, and terminology in the existing literature. For example, just some of the terms describing weakness syndromes in the ICU and the associated acronyms include critical illness polyneuropathy (CIP or CIPN), neuromuscular disorders (NMDs), acute quadriplegic myopathy (AQM), critical illness neuromuscular abnormalities (CINMAs), and ICU-acquired paresis (ICUAP). To complicate matters further, studies suggest that patients diagnosed with critical illness polyneuropathy (CIPN) may in fact have myopathy as a contributing if not primary cause of weakness. This has lead to the coining of an additional term, critical illness polyneuropathy and myopathy (CIPNM), which reflects the difficulty discriminating between myopathic and neuropathic causes of weakness syndromes acquired in the ICU. Last, although the so-called acute quadriplegic myopathy (AQM) first described in patients with severe acute asthma and other types of respiratory failure has often been described as a distinct entity, there is overlap between AQM and CIPNM. Given the above caveats, this update focuses on three causes of severe, diffuse weakness in the ICU: prolonged neuromuscular blockade, CIPNM, and AQM, and discusses the shared and unique features of these disorders. Our goal is to increase aware-