1. Introduction
Sporadic inclusion body myositis (IBM) is a rare acquired idiopathic inflammatory myopathy with autoimmune and neurodegenerative features that is characterized by slowly progressive asymmetric weakness of the proximal lower extremity (quadriceps) or distal upper extremity (wrist and distal phalangeal flexors) without sensory deficits (1, 2). IBM is most commonly observed in men over fifty years of age. The incidence of IBM is approximately 8 per million in the United States (3) and ranges between 2 and 12 per million in other parts of the world (1, 4). The slow onset of the disease often delays its diagnosis for several years (5). Involvement of the quadriceps muscle group contributes to gait instability and falls in the vast majority of patients (6). Oropharyngeal dysphagia also occurs frequently and increases the risk of aspiration in patients with IBM because clearance of secretions may be impaired (7, 8). In contrast to other inflammatory myopathies (e.g., polymyositis, dermatomyositis), intrinsic pulmonary disease (e.g., interstitial pneumonitis, alveolitis) and myocardial fibrosis complicated by arrhythmias or heart failure does not occur in IBM1.Nevertheless, diaphragmatic dysfunction may contribute to respiratory insufficiency in some patients with IBM (9).
A clinical history of weakness exceeding twelve months in duration, elevated plasma creatine phosphokinase concentration, and muscle histology demonstrating endomysial inflammation, rimmed vacuoles, and amyloid or other protein deposition are required to establish the diagnosis of IBM (10). Magnetic resonance imaging may also provide confirmatory evidence of the disease (11). The etiology of IBM remains undefined, but autoimmunity against cytosolic 5'-nucleotidase 1A has been implicated in the disease's pathophysiology (12). Coincident autoimmune diseases (e.g., systemic lupus erythematosus, Sjogren’s syndrome, sarcoidosis) may also be present. A neurodegenerative cause of IBM has also been proposed for which considerable indirect evidence exists (1). Treatment for IBM is entirely supportive because the disease is essentially unresponsive to the immunosuppressive therapies used to manage other inflammatory myopathies (13-15). Few reports exist that comment on the anesthetic considerations of IBM, but concern about the potential for exaggerated sensitivity to neuromuscular blockers and respiratory compromise has been consistently expressed. The authors describe their perioperative management of an elderly man with IBM undergoing urgent surgery after sustaining orthopedic trauma and discuss the anesthetic ramifications of the disease.
2. Case Presentation
An 81-year-old, 77 kg, 183 cm man with a three-year history of muscle biopsy-proven IBM suffered a left intertrochanteric femoral fracture and a small parafalcine subdural hematoma as a result of falling down stairs in his home. The patient originally had progressive left proximal lower extremity and bilateral distal upper extremity weakness (left > right) that began several years before the diagnosis was definitively established with a muscle biopsy. The patient's serum creatine phosphokinase concentration was 748 U/L (normal < 170 U/L) at the time of the diagnosis. The patient had several near falls in the months preceding the accident. His left hand and wrist weakness affected his activities of daily living to some degree (fine motor skills), but physical and occupational therapy helped the patient remain active and he continued to live independently with occasional assistance from his wife. Because of worsening left quadriceps weakness, he had recently begun using a cane to help him rise from a seated position. The patient had a history of oropharyngeal dysphagia (solid food, pills) for which he was receiving care from an otolaryngologist. The patient also had chronic gastroesophageal reflux disease that was well controlled with a proton pump inhibitor. He did not have difficulty swallowing liquids and denied respiratory complaints associated with chronic aspiration. The patient did not lose consciousness after striking his head on the stairs and had no new neurological complaints. His other past medical history was notable for coronary artery disease, hyperlipidemia, chronic low back pain, and vertebral artery stenosis. He underwent coronary artery bypass graft surgery 16 years before the current admission. A previous transthoracic echocardiography revealed normal left ventricular systolic function. He denied chest pain, dyspnea, and exercise intolerance. The physical examination and radiographs of his femur revealed the left intertrochanteric fracture. The Glasgow coma scale was 15 and there were no new focal neurological deficits. A magnetic resonance imaging study demonstrated the small parafalcine subdural hematoma without a cerebral mass effect.
The patient was transported to the operating room for repair of the left intertrochanteric fracture. Because primary respiratory failure (16, 17) resulting, at least in part, from diaphragmatic dysfunction (9) has been previously reported in patients with IBM and prolonged duration of action of neuromuscular blockers may also occur, the authors opted to avoid the use of a neuromuscular blocker for endotracheal intubation and during maintenance of anesthesia in the current patient. After applying cricoid pressure, anesthesia was induced using intravenous lidocaine (0.5 mg.kg-1), propofol (1 mg.kg-1), and remifentanil (infusion of 0.1 mcg.kg-1.min-1). Manual positive-pressure ventilation with sevoflurane (inspired concentrations between 2% and 3%) in oxygen (100%) was used with sustained cricoid pressure to supplement to intravenous anesthetics after loss of consciousness. After uneventful endotracheal intubation, anesthesia was maintained with sevoflurane (end-tidal concentrations between 0.7% and 1.5%) and remifentanil (infusion rates of 0.05 to 0.15 mcg.kg-1.min-1). The orthopedic surgeon repaired the fracture with a trochanteric femoral nail. Intravenous acetaminophen and fentanyl were administered for postoperative analgesia. The patient tolerated the procedure well. He demonstrated vigorous spontaneous respiratory effort as he emerged from anesthesia and was extubated without difficulty in the operating room. The patient made an uncomplicated recovery from surgery and was subsequently transferred to a rehabilitation facility in stable condition.
3. Discussion
Only a few reports have described the anesthetic implications of IBM, which is somewhat surprising considering that patients with this disease often sustain injuries as a result of falls (6) or require cricopharyngeal procedures (e.g., surgical myotomy, botulinum toxin injection) for treatment of oropharyngeal dysphagia (7, 18, 19). Ntatsaki et al. discussed their anesthetic technique for a patient with IBM who required serial electroconvulsive therapy (ECT) for treatment of severe psychotic depression (20). These authors used a reduced dose of mivacurium to facilitate endotracheal intubation during each ECT because they were concerned about sensitivity to neuromuscular blockers and postoperative respiratory complications. The approach provided satisfactory intubating conditions, but it did modestly delay emergence after ECT because the duration of neuromuscular blockade exceeded the length of the short procedure. The patient suffered no adverse sequelae. In contrast, two reports published in the Japanese literature emphasized that IBM may be associated with postoperative pulmonary complications after general anesthesia. Igari and colleagues used a reduced dose of rocuronium in a patient with IBM undergoing video-assisted thoracic surgery during propofol-remifentanil anesthesia because they were concerned about postoperative respiratory depression (21). Indeed, the authors were unable to extubate their patient after reversal of neuromuscular blockade, most likely because of underlying pulmonary dysfunction related to IBM. Similar to the authors’ approach in the current patient, Nakano et al described endotracheal intubation without the use of a neuromuscular blocker after induction of general anesthesia in an elderly man with IBM undergoing a jejunostomy, but this patient developed postoperative aspiration pneumonia (22). The current patient did not have a history of compromised pulmonary function and was easily extubated after surgery. His oropharyngeal dysphagia also did not interfere with his ability to swallow liquids nor did he describe a history consistent with chronic aspiration. Indeed, he did not develop aspiration pneumonia after surgery. Marinho et al. reported a unique approach to anesthesia in a patient with IBM who underwent percutaneous thoracic vertebral kyphoplasty in prone position (23). This patient required chronic non-invasive ventilation because of poor respiratory function. The patient’s intraoperative care was managed using epidural anesthesia, conscious sedation, and bi-level positive airway pressure. In this case, the authors (23) avoided endotracheal intubation entirely because they were concerned that the patient’s preexisting respiratory dysfunction may preclude their ability to wean the patient from mechanical ventilation after the procedure.
The current and previous (20-23) cases used reduced doses of or completely avoided neuromuscular blockers in patients with IBM because of theoretically enhanced sensitivity to these drugs, but with the exception of anecdotal experience, there are no data to definitively establish the pharmacokinetics, pharmacodynamics, and relative safety of neuromuscular blockers in this setting. The actions of neuromuscular blockers may be prolonged in other forms of inflammatory myopathy, but this contention has not been examined systematically in controlled clinical trials and remains controversial, in part because inflammatory myopathies including IBM may not affect the functional integrity of the neuromuscular junction (1). Flusche et al. reported that recovery from vecuronium was significantly delayed in an elderly man with polymyositis (24), but Brown et al. reported that the durations of action of succinylcholine and atracurium both fell within the normal range in a woman with dermatomyositis (25). Johns et al. described an abnormal contracture response to succinylcholine in a 2 year-old boy with dermatomyositis, but the duration of action of the depolarizing neuromuscular blocker was not prolonged (26). A rise in serum potassium concentration was also observed in this case, but the effect was not overly exaggerated (26), suggesting that succinylcholine may not precipitate dangerous hyperkalemia in patients with inflammatory myositis. Nevertheless, the use of succinylcholine is relatively contraindicated in patients with other primary muscle diseases because of an exaggerated hyperkalemic response (27), and for this reason, the authors did not use the depolarizing neuromuscular blocker in the current patient.
In summary, there is a lack of consensus about the use of neuromuscular blockers in patients with IBM and other inflammatory myopathies. The authors avoided these drugs and were able to easily secure the patient’s airway and maintain adequate muscle relaxation using a balanced sevoflurane-remifentanil anesthetic. The current patient did not have difficulty swallowing liquids or handling secretions despite his oropharyngeal dysphagia nor did he have a history of aspiration, respiratory insufficiency, or diaphragmatic dysfunction. The presence of any of these IBM-related conditions most likely would have prompted the authors to secure the patient’s airway using a neuromuscular blocker despite the theoretical risk for a prolonged duration of action. Clinical trials are necessary to define the pharmacology of neuromuscular blockers in patients with IBM and determine whether use of these drugs contributes to postoperative respiratory insufficiency in these vulnerable patients.
