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Although not often performed, the gold standard for diagnosing critical illness neuropathy remains electrodiagnostic testing, which includes nerve conduction studies and needle electromyography. This activity describes the invaluable electrodiagnostic findings of nerve conduction tests and needle electromyography studies. It also highlights the role of the interprofessional team in evaluating patients with intensive care unit–related critical illness neuropathy. Objectives: Identify the indications for electrodiagnostic testing in critically ill patients. Assess the nerve conduction study findings in a patient with critical illness neuropathy. Assess the electromyographic findings in a patient with critical illness neuropathy. Communicate the importance of collaboration among the interprofessional team to enhance care delivery for patients with critical illness neuropathy. Access free multiple choice questions on this topic.

As medicine advances, more critically ill patients are surviving longer intensive care unit (ICU) admissions. Patients with sepsis, multiorgan failure, severe burns, prolonged mechanical ventilation, and polypharmacy often develop profound neuromuscular weakness during their hospitalization despite appropriate medical interventions and treatments. Often referred to as "ICU-acquired weakness" (ICUAW), this underdiagnosed condition most commonly results from a spectrum of critical illness polyneuropathy (CIP), critical illness myopathy (CIM), or a combination of both. While CIP and CIM often occur simultaneously, it is important to understand the key features of each condition to ensure prompt recognition, prevent further disability, and ensure better patient outcomes.[1][2] While the conditions are often underdiagnosed, studies show that the incidence of ICUAW in patients with greater than 7 days of mechanical ventilation may range from 25% to 83%. [3] Critical illness neuropathy (CIN) may be evident as a patient fails to wean off the ventilator or if the patient has profound weakness or numbness in extremities upon awakening from sedation. Upon leaving the ICU, a physical exam may also reveal diminished deep tendon reflexes, possible muscle atrophy, or balance impairment. The bulbar and extraocular muscles are often spared in CIP.[4] Laboratory studies such as cerebrospinal fluid are usually normal; this may help differentiate the condition from other illnesses with similar presentations, such as Guillain-Barre Syndrome.[5] Creatine phosphokinase (CPK) is within normal limits in CIP and can become elevated in CIM. Systemic inflammatory response syndrome (SIRS) or sepsis is the most frequent underlying factor in CIP (as opposed to the use of neuromuscular blocking agents and steroids, which predominate in CIM).[6]

Critical illness neuropathy (CIN) may be evident as a patient fails to wean off the ventilator or if the patient has profound weakness or numbness in extremities upon awakening from sedation. Upon leaving the ICU, a physical exam may also reveal diminished deep tendon reflexes, possible muscle atrophy, or balance impairment. The bulbar and extraocular muscles are often spared in CIP.[4] Laboratory studies such as cerebrospinal fluid are usually normal; this may help differentiate the condition from other illnesses with similar presentations, such as Guillain-Barre Syndrome.[5] Creatine phosphokinase (CPK) is within normal limits in CIP and can become elevated in CIM. Systemic inflammatory response syndrome (SIRS) or sepsis is the most frequent underlying factor in CIP (as opposed to the use of neuromuscular blocking agents and steroids, which predominate in CIM).[6] Although not often performed, the gold standard for diagnosing critical illness neuropathy remains electrodiagnostic testing, which includes nerve conduction studies and needle electromyography. It should be noted that while EMG is the optimal way to diagnose CIP, there are many challenges to performing a complete study in ICU conditions, including electrical interference, anasarca, hypothermia, peripheral edema, or limited patient participation in the exam. Nevertheless, electrodiagnostic testing is an essential tool in evaluating profound weakness in the ICU setting that can direct the clinical team in determining further management. Pathophysiology of CIP and CIM The etiology of CIP and CIM is not entirely clear, but it is considered complex and multifactorial. Ultimately, it leads to axonal dysfunction, ischemia, and degeneration, necessitating aggressive treatment of underlying medical causes and physical neurorehabilitation. It is thought to be related to abnormal vascular, metabolic, and electrical processes leading to motor or sensory neuron abnormalities: Vascular: Vascular autoregulation leads to increased microvascular permeability (eg, dilation of vessels), which can result in edema, hypoxemia, proinflammatory invasion of leukocytes and cytokines, and occlusion within the muscle-neuron units Metabolic: Metabolic generation of reactive oxygen and nitric oxide species, failure of mitochondrial repair, neuronal hyperglycemic damage, and hypoalbuminemia

Vascular: Vascular autoregulation leads to increased microvascular permeability (eg, dilation of vessels), which can result in edema, hypoxemia, proinflammatory invasion of leukocytes and cytokines, and occlusion within the muscle-neuron units Metabolic: Metabolic generation of reactive oxygen and nitric oxide species, failure of mitochondrial repair, neuronal hyperglycemic damage, and hypoalbuminemia Electrical: Electrical disruption of sodium and calcium channels and loss of cellular excitability Clinical and Histopathological Features of CIP and CIM CIP Predisposing factors for CIP include sepsis with concurrent encephalopathy, recurrent exposure to nondepolarizing neuromuscular blocking agents, and multiorgan failure. Clinical and histopathological features of CIP include: Presence of diffuse paraparesis or paraplegia, more distal than proximal, with preserved muscle bulk or mild atrophy Early loss of deep tendon reflexes or areflexia Long-standing difficulty weaning mechanical ventilation after exclusion of cardiopulmonary etiologies Electrodiagnostic evidence of axonal sensorimotor polyneuropathy CIM Predisposing factors for CIM include recurrent exposure to neuromuscular blocking agents, severe asthma, pneumonia, prolonged acidemia, acute respiratory distress syndrome, prolonged high-dose corticosteroid use, prolonged use of aminoglycosides, sepsis, multiorgan failure, and organ transplantation. Clinical and histopathological features of CIM include: Presence of diffuse paraparesis or paraplegia, more proximal than distal, with severe atrophy Delayed loss of deep tendon reflexes Long-standing difficulty weaning mechanical ventilation after exclusion of cardiopulmonary etiologies Electrodiagnostic evidence of motor unit and recruitment abnormalities as well as an absence of excitability with muscle stimulation, with possible preservation of sensory potentials Biopsy of type II atrophic myofibers on hematoxylin and eosin (H&E) stain and myofiber necrosis may be performed to aid in diagnosis.

Often, patients with prolonged ICU admission develop profound weakness or failure to wean off a ventilator. Intensivists, physiatrists, and neurologists must recognize that further evaluation with electrodiagnostic testing is warranted in these circumstances. As healthcare professionals, appropriate disease recognition and diagnosis of critical illness neuropathy helps expedite patient recovery and can improve long-term quality of life. While there is a vast differential in the patient with weakness that develops in the ICU, nerve conduction and EMG studies may be able to identify the etiology and further guide the management. Once the diagnosis of CIN is made, the interprofessional team must include an interprofessional team of physicians, physical therapists, occupational therapists, speech therapists, nutritionists, social workers, and case managers. These professionals can work together to coordinate early mobilization and aggressive multifaceted rehabilitation. Typically, there is a long and challenging recovery ahead for patients with CIN upon leaving the critical care setting. The best patient outcomes are achieved with a coordinated effort between the various medical disciplines and departments.[2][13]