A 51-year-old woman with antibody-positive myasthenia gravis, on immunosuppressive therapy with azathioprine, is admitted to the intensive care unit for increased work of breathing. Two weeks prior she had an upper respiratory tract infection, and when it did not improve, she was prescribed a course of levofloxacin, which she started 3 days ago. Since that time she has had a progressive dyspnea and was unable to walk up a flight of stairs. Her initial vital signs in the emergency department (ED) were normal and her oxygen saturation was 98% on room air with a respiratory rate of 24. She appeared comfortable, and although tachypneic she did not have accessory muscle use. She underwent bedside spirometry testing and was found to have a negative inspiratory force of −40 mm Hg and forced vital capacity of 0.75 L (weight 79.6 kg). An arterial blood gas was obtained in the intensive care unit and was:
Should this patient be intubated?
Correct Answer: D
This patient is presenting with myasthenic crisis, which can occur for a number of reasons, most importantly for this patient likely secondary to infection and use of a fluoroquinolone antibiotic. Other common medications that can worsen myasthenia include macrolides, aminoglycosides, beta-blockers, magnesium-containing medications, and steroids. Early initiation of noninvasive ventilatory support with BiPAP may avert the need for endotracheal intubation. Although there are no strict guidelines on admission criteria into the intensive care unit, close respiratory monitoring is needed as these patients can quickly develop hypercarbic respiratory failure and require endotracheal intubation. The assessment of respiratory function included the bulbar muscular function as those with bulbar weakness may have overt aspiration. Signs of respiratory weakness including hypophonia, pausing while talking to breathe, rapid/shallow breathing, and paradoxical abdominal breathing. The two commonly used bedside tests are the vital capacity and negative inspiratory force. Consideration for intubation should occur if the vital capacity falls below 15 to 20 mL/kg (ideal body weight) or the negative inspiratory force is less than −25 to −30 mm Hg. These values should not be taken in isolation the clinical context, which needs to be evaluated as well. This patient does not require intubation at this time, but if progression of her weakness were to occur intubation with either a nondepolarizing agent (eg rocuronium) or depolarizing agent (eg succinylcholine) can be used, but nonstandard dosing needs to be considered. Given there is decreased functional acetylcholine receptors, there is a need for a higher dose of depolarizing agents and decreased dosage of nondepolarizing agents. Given the sensitivity and unpredictable response to nondepolarizing agents, depolarizing agents are typically used.
A 14-year-old woman with medically intractable epilepsy presents to ED in status epilepticus. Three weeks prior, she had a “virallike illness” and had never fully returned to normal. She was having increased seizure frequency during that time. While in the ED, she was intubated for airway protection. Her workup reveals pyelonephritis, and she is treated with an appropriate course of antibiotics with improvement in her vitals and laboratory results. She had limited improvement in her mental status initially, and long-term electroencephalogram (EEG) monitoring revealed subclinical status epilepticus. Following 24 hours of burst suppression with propofol and midazolam, she had improvement in her EEG. Over the course of the next 72 hours, she had improvement in her mental status but was unable to be weaned from the ventilator because of poor tidal volumes during spontaneous breathing trials. On examination, she has marked proximal weakness in all four extremities. Electodiagnostic testing is completed, which demonstrates prolonged compound muscle action potential (CMAP) on nerve conduction studies and positive sharp waves and decreased recruitment on electromyography.
What is the MOST likely cause of her weakness?
Correct Answer: B
The patient has quadriparesis including respiratory weakness with electrodiagnostic testing consistent with a myopathic disease process. Given her recent intubation, sedation, sepsis, and limited mobility due to burst suppression, these point to critical illness myopathy as the underlying disease process. Risk factors for critical illness myopathy include sepsis, high-dose glucocorticoids, prolonged neuromuscular blockade, hyperglycemia, immobility, vasopressor use, renal replacement therapy, and trauma. In critical illness neuropathy, the common findings are decreased amplitude of both sensory and motor nerve responses with normal spontaneous activity on EMG. Although not required to make the diagnosis, muscle biopsy in critical illness myopathy will typically demonstrate loss of myosin. There are no specific treatments for critical illness myopathy although strict glucose control can decrease the risk and early mobility may improve function. Although the patient had a “virallike illness” before her presentation, the nerve conduction findings are not consistent with a demyelinating disease process such as GBS. Although ADEM can present with quadriparesis due to high cervical cord involvement, the nerve conduction findings are not consistent with this diagnosis. Although an inflammatory myopathy is unlikely the cause, given her other ongoing critical illness.
A 56-year-old man with essential thrombocytosis (baseline approximately 800 000) and prior renal cell carcinoma status post left nephrectomy 5 years before presentation presents with progressive bilateral lower extremity weakness and ascending paresthesia over the course of 7 days. He has mild proximal weakness in his bilateral legs, but is able to ambulate, and decreased sensation in his bilateral legs to mid-shin. No reflexes noted on examination. Additional testing including a lumbar puncture, demonstrating elevated protein with no white blood cells, and nerve conduction study, demonstrating dispersion of motor and sensory nerve responses with conduction block, confirms the diagnosis of GBS.
What is the most appropriate treatment?
There are several types of GBS, classified by the part of the peripheral nerve involved in this disease. Acute inflammatory demyelinating polyradiculoneuropathy (AIDP) is the most common etiology, but there is also an axonal type, which typically results in worse recovery. This patient presents with the stereotypical presentation of GBS: ascending paresthesias, progressive ascending weakness, and loss of deep tendon reflexes. Confirmatory testing includes lumbar puncture, which demonstrates a cytoalbuminologic gap and nerve conduction study suggestive of demyelinating features. Although not presented in the case, there are a number of disease-related complications including labile blood pressure, arrhythmias, gastroparesis, urinary retention, and syndrome of inappropriate antidiuretic hormone (SIADH). Treatment of GBS has two treatments: IVIg and PLEX. The American Academy of Neurology recommendations for treatment of GBS in ambulatory patients within 2 weeks of neuropathic symptoms advocates for PLEX. Another reason for use of PLEX over IVIg in this patient is the complications of treatment. IVIg can results in thrombosis because of hyperviscosity. Given his underlying thrombocytosis, IVIg could place him at even higher risk worsening thrombocytosis and in turn increase the risk of bleeding especially with platelet counts over 1 000 000. Studies showed that sequential treatment with PLEX followed by IVIg does not have a greater benefit than either treatment given alone. In addition, AAN guideline does not recommend steroids for the treatment of GBS patients (Level A, Class 1).
A previously healthy 36-year-old male was admitted to the medical intensive care unit following a cardiac arrest. On the day of admission to the hospital, he was getting ready for work, but felt quite fatigued and short of breath. He was talking with his wife, and she noted that he looked “blue” and then fell to the floor. He did not have a pulse, and she started emergency medical services (CPR) and contacted emergency medical services (EMS). On arrival, he did not have a pulse and received one dose of epinephrine and was intubated in the field with return of spontaneous circulation. On arrival to the ED, he was hemodynamically stable with normal vital signs, localizing with his arms and opening his eyes to noxious stimulation. He remained intubated and his mental status recovered, but he was unsuccessfully extubated because of hypercarbic respiratory failure over the course of several hours. A full cardiac and pulmonary workup was completed without underlying etiology for his respiratory failure. The neurology serviced was consulted for evaluation of failure to wean. Further history noted progressive dyspnea and fatigue over the last 6 months, but he attributed this to his stress at work. Also, he noted more difficulty with lifting his young children. His neurologic examination was pertinent for mild symmetric deltoid weakness and moderate symmetric hip flexion weakness. The remainder of the neurologic examination was normal. Electrodiagnostic tests were completed with normal nerve conduction studies, but abnormal electromyography with positive sharp waves and fibrillation potentials demonstrated in the deltoid, supraspinatus, iliopsoas, and thoracic paraspinal musculature. The paraspinal musculature also demonstrated complex repetitive discharges and myotonic discharges.
What is the MOST likely underlying cause of the patient’s presentation?
Correct Answer: A
The neurologic etiologies of failure to wean from the ventilator are quite broad and can be divided into central (bihemispheric, bithalamic, brain stem, and cervical cord), peripheral nerve, neuromuscular junction, and muscle. The pattern of weakness can help determine the underlying etiology, and electrodiagnostic tests can further determine the underlying cause. In this case, examination demonstrates myopathic pattern of weakness and this is confirmed with the electrodiagnostic testing. The patient has a limb-girdle pattern of weakness with the striking finding of abnormal electromyography within the paraspinal muscles. The clinical history and EMG findings are most consistent with late onset Pompe disease, which is a deficiency in acid maltase. Although muscle biopsy can confirm the diagnosis, there are now blood tests: leukocyte isolates from whole blood for GAA activity and blood spot assay for acid alphaglucosidase activity. Making this diagnosis is crucial as there is enzyme replacement therapy which can improve survival. C9orf72 genetic mutation is associated with ALS-FTD spectrum disorders. Glucose-6-phosphatase deficiency is associated with von Gierke disease, which presents in infancy with hepatosplenomegaly, hypoglycemia during fasting, epilepsy, and lactic acidosis. Laminin A/C is associated with limb-girdle muscle dystrophy, which can present similar but will not have the respiratory and paraspinal muscle findings as Pompe. Zinc finger 9 is associated with myotonic dystrophy type 2 that has a very characteristic “hatchet face” appearance and myotonia on examination.
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