Good day everyone, I am Hannah Nobleza, the Medical Director of the Neurocritical Care Service in Baptist Memorial Medical Center in Memphis, Tennessee, and I am here to talk about the neuromuscular disorders in critical care. I have no disclosures. My objectives are as follows. To describe the key concepts and comprehensive assessment and management of the critically ill patients with neuromuscular disease and to apply the principles and concepts for the clinical evaluation and management of patients with neuromuscular disorders as it applies to neurocritical care. As you all know, the polio outbreak in the 1950s is one of the worst epidemics in the United States. This virus was eradicated, but it is one of the known acquired neuromuscular conditions that were treated in the ICU. While 30% of mechanically ventilated patients can develop clinically overt weakness, while 28% of patients in the ICU with a complaint of weakness probably had an established neuromuscular disorder. So this is why it's important to know how to manage neuromuscular diseases in the critical care setting. We have here a 37-year-old woman with a history of myasthenia gravis who is on prednisone. Her main complaint coming into the ER was worsening shortness of breath, which has been going on three days ago since after a respiratory infection. In addition to that, she has been showing signs of aspiration. When encountering any neuromuscular case for the boards, the basic process for analyzing the case should be as follows. You assess the patient in the question, in the vignette, is she stable or not? Do you need to stabilize the patient first, or can you continue data gathering? After stabilization and data gathering, then you can decide both on empiric therapy and targeted therapy, and also consider how you are going to support the patient through the neuromuscular illness, as well as other medical conditions. Then as the patient stabilizes and recovers, rehabilitation is now considered. For this patient, she was the one giving the history, but there might be signs that we have to look closer at to see if she is stable. In this case, the patient is tachycardic. She was able to give her story, but clearly having a hard time. Her axial muscles are weak, and there's some bulbar involvement. She has intact reflexes. In the boards for the case vignette, if the question is what you will do next, you should first assess ABCs and subsequently manage that. The history taking at this time should be brief, and as you go through the vignette, you have assessed for signs of impending decline. In reality, this will be the same approach you would have done for the patient anyway. Get a brief history, and while you are getting that, you're assessing for signs that you might need to intervene sooner or later to secure the airway, breathing, and circulation. For neuromuscular disorders, there are several key points in the history taking that you have to keep in mind as you go through these case vignettes. There may be some key features in the history that the vignette might be giving you cues about, so you can narrow your diagnosis. I listed here several points of each component of the history that you may need to look out for. For example, demographic information may give you a cue on the sex and age predisposition of certain conditions. A highlighted, fluctuating progressive condition may cue you into thinking of myasthenia rather than Guillain-Barre syndrome. The presence of constitutional symptoms and a suspicion of malignancy can cue you towards thinking of a perineoplastic cause of neuropathy. Poor cooking practices or exposures to canned or homemade jams may lead you to think of botulinum toxin as the etiology of your neuromuscular condition. After the history, now we have to look at the key points of the examination for neuromuscular conditions. As I mentioned a while ago, after you go through the ABCs and the patient is stable, you can go through a focused neurologic exam or take in highlights of the neurologic exam in your case vignette. For the purpose of the boards, they may not give you a specific indication that you're dealing with a neuromuscular condition, so you will have to localize the lesion. And for you to be able to do that, you have to go through these key elements of the neurologic exam. Is the patient awake? Is the patient the one giving you the history in the vignette? Is the patient aphasic? If the patient is aphasic, then that aphasia localizes to the cortex, so you will probably move your localization to the left hemisphere of the brain if the vignette suggests that. But otherwise, if the vignette gives you a talking patient with cranial nerve weakness and all extremity involvement, then you will have to gather more highlighted information in the test like the distribution of weakness, the pattern of weakness. Is it symmetric, asymmetric? Does it involve axial muscles only? Does it involve distal muscles more than the axial muscles? Are there abnormal reflexes such as up-going toes that may change your localization to an upper motor neuron pathology? Is sensation impaired with all extremity weakness? Then you may be dealing with a quadriparetic patient with sensory involvement, then it might be a GBS variant with sensory involvement depending on the history. So going back to our case, we can see someone who has a history of myasthenia with a recent viral infection and is now having worsening shortness of breath and possible aspiration demonstrated by her coughing. The examination shows someone who is mildly in distress with tachypnea. She has weak axial muscles with some vulvar involvement and has generalized weakness with no up-going toes. So as we go through this vignette, we know that the patient is giving the history but is having difficulty, so she's awake and her difficulty is more because of pulmonary issues than an actual language problem. The distribution of weakness is generalized in the extremities with axial and cranial nerve involvement, so this is likely her myasthenia gravis flare. When we localize the lesion, this is where we have to apply where the lesion is based on the history and physical exam. For this patient with all extremity involvement with axial muscles and cranial nerve involvement, it is most likely something that involves all nerves or muscles, then one side of the brain or spinal cord. Since the physical exam demonstrates generalized involvement. Then as you go through the vignette, you further want to confirm your suspicions that this is a lower motor neuron problem by looking at other signs such as hyperreflexia, hypertonia, up-going toes that will make you localize the upper motor neuron lesion, meaning it's a damage to the motor neurons before the nuclei of the cranial nerves or the anterior horn cells of the spinal cord. This table gives you a guide of localization level findings. For example, patients with acute hemiparesis that can be attributed to a Vassar syndrome in the brain is likely a brain infarction, which is an upper motor neuron lesion. If a patient involves both lower extremities and both toes are up-going, the lesion can be localized to the spinal cord. This continues on to describe the physical exam pattern for peripheral nerve pathologies, neuromuscular junction, muscle, and generalized involvement of all muscles. So for our case, where is the lesion? Given the history in the physical exam, most especially the fluctuating course and with the history of myasthenia gravis, this is likely a myasthenia gravis flare, which is in the neuromuscular junction. A very important component of neuromuscular conditions is how it affects the respiratory function. The mechanisms of respiratory failure are as follows. If someone has oropharyngeal weakness due to cranial nerve involvement, they can have aspiration, recurrent weak cough, hypophonic voice, and a primary airway failure can happen as well as diaphragm failure. Some may become more prominent, like these symptoms can be more prominent when you start decreasing ventilatory support, while some patients can present with primary lung issues such as a difficult to wean patient and you may have to consider a neuromuscular condition. Our general considerations for intubation include decreased consciousness, known course, and signs of progressive generalized muscle weakness, inability to manage secretions associated with dyspnea on exertion. The 20-30-40 rule pertains to the typical values of the vital capacity, mean inspiratory pressure, and the maximal expiratory pressure. The force vital capacity is the largest volume of gas that the patient can exhale. So it actually measures the exhaled volume maximally after you take a full breath in. And then the MIP, or the maximal expiratory pressure, is commonly known as the NIF, or the negative inspiratory force. So it measures the maximal amount of negative pressure that we can generate, and it actually measures primarily the diaphragm. The maximal expiratory pressure, on the other hand, is the greatest amount of positive pressure that you can generate. So it measures the expiratory muscles. So the 20-30-40 rule refers to a vital capacity of less than 20 milliliters per kilogram, an MIP, or an MIP of less than 30 centimeters water, or the maximal expiratory pressure of less than 40 centimeters water, as a basis of intubation. However, we shouldn't be intubating a patient solely based on the numbers. These are good numbers to remember in addition to other indications that may help the decision to intubate. Some of the other signs of respiratory distress are indicated here. So if a vignette does mention some of these values, it is possible that they want you to keep in mind that you might have to consider a higher level of care for a patient, or that you need to monitor the patient really closely. Going back to our case, what are the possible etiologies of a neuromuscular junction defect? So you can use this table to give you a list of the possible differential diagnosis per level of pathology, but specifically for the neuromuscular junction, you can see here that the possible differential diagnosis if you localize a lesion into the neuromuscular junction are myasenia, botulinum, depending on the history. This next table is useful for vignettes that might ask you about a specific part of the neuromuscular junction that is affected by certain disease states. So if you have a history of a patient who ate home, made jams, who presents with descending paralysis, you have to confirm your diagnosis with a stool toxin and know that the defect is in the presynaptic part of the neuromuscular junction, and we're talking about the botulism. For neuromuscular cases, these are generally the diagnostic testing that we usually do or recommend, but just to briefly state, specifically for neuromuscular junction cases, repetitive nerve stimulation test is a specific EMG test to evaluate the neuromuscular junction disease. It can differentiate between presynaptic and postsynaptic conditions. And then the antibody serum testing, depending on the pathology or the case that you're looking at, there are, for example, for myasenia, there are antibody-negative myasenia gravis, but for the purpose of the boards, if the clinical vignette is on myasenia, it most likely will involve known antibodies. So for example, you should know that if they mention primarily cranial nerve involvement, the antibody associated with that is an anti-musc antibody. The other general categories of neuromuscular conditions in the ICU are indicated here. For Guillain-Barre syndrome, the main pathology is autoimmune, and it's typically symmetric. And unlike botulism, it is ascending, symmetric, love-stalking pattern of paralysis with areoflexia. And the most common variant is acute inflammatory demyelinating polyneuropathy, or AIDP. West Nile-associated acute flaccid paralysis is also immune-mediated, but the affected part are the spinal motor neurons. These are usually asymmetric, with the CSF-IgM West Nile virus being positive. Because the tests can come back later, sometimes these patients can mimic Guillain-Barre syndrome and can actually receive the treatment for it. And then the test will come back positive for West Nile from the CSF. Similar to the ICU-acquired weaknesses, there's no real treatment for West Nile virus. It's mainly supportive. And for the critical, for ICU-acquired weaknesses, this encompass critical illness polyneuropathy and critical illness myopathy. And the main treatment is really to mobilize the patient in supportive care. Going back to our neurologic physical exam, for electrolyte-associated neuromuscular disorder, as you see here, they may come with a general neurology program, such as seizures or coma, but may be generally weak. And if you do not have a good reason for the weakness after a workup, you can consider these electrolyte abnormalities as the etiology of the neuromuscular weakness. Just to highlight, hypophosphatemia can cause proximal myopathy. Severe hyponatremia, as we're familiar with, can present as seizures first. And hypermagnesemia, typically seen in the setting of preeclampsia, when they get supernormal magnesium targets, the effect of that can be seen as hyporeflexia. In summary, the approach to neuromuscular disorders in the critical care setting should be systematic. Airway-breathing circulation is still our main priority as we try to determine the possible neuromuscular condition. And the reason why the approach should be systematic is we would want to be able to localize the lesion properly to be able to come up with a diagnostic and appropriate therapeutic plan for the patient. Thank you and good luck in the boards.

neuromuscular disorders

critical care

respiratory function

case vignettes

neurological exam