 Welcome to meningitis part 1. In this section, we will discuss the pathophysiology and presentations of meningitis and encephalitis. Meningitis and encephalitis are infections of the central nervous system. Meningitis primarily affects the meninges. Encephalitis is confined to the brain parenchyma. If left untreated, meningitis and encephalitis cause a significant CNS dysfunction and sepsis, leading to lifelong neurological disabilities and even death. Therefore, there are both must-not-miss diagnosis in the emergency department. We'll talk about the pathophysiology of these two diseases. In terms of meningitis, it can be caused by bacteria, viral and other causes. The main one we need to concern ourselves with would be meningitis caused by bacteria. Organisms enter the meninges through the bloodstream from other parts of the body. The main bacteria include strep pneumoniae, myserium meningitis and hemophilus influenza. All these bacteria are part of the normal flora in the upper respiratory tract. Viral meningitis are usually caused by antrovirus and HSV, or the herpesimplex virus. Common causes for meningitis include TB, Lyme disease and others. Encephalitis is usually caused by virus. They include the herpesimplex virus, varicella zoster virus, measles and others. In terms of at-risk population, as with most infection, they include patients who are immunocompromised such as those on chemotherapy, malnutrition, chronic sterile use and those who have not been vaccinated. Another reason is if there is any break in the blood-brain barrier, the bacteria are more likely to invade. They include reasons such as surgery, trauma including basal skull fracture, or indwelling hardware such as VP shunts. Let's move on to presentation. In terms of history, patients with meningitis may complain of fever, headache, neck stiffness or pain. Although less than 50% of patients have this classic triad for meningitis, particularly if it is early. The associated symptoms include decreased level of consciousness, either into confusion or lethargy. They can also include nausea, vomiting and photophobia. Atypical symptoms can also occur particularly in the elderly or infants. These two groups might only have lethargy or decreased level of consciousness without headache or neck pain. For encephalitis, the symptoms are quite similar. The patients can complain of headache, fever, although neck pain is not as prominent since the meninges are not involved. They can also have decreased level of consciousness, confusion or seizures. As with all infectious diseases, it is also important to ask about travel, any sick contacts and particularly if there is an outbreak in where they live. On physical examination, we pay special attention to the vital signs. They may have fever or signs of sepsis such as tachycardia or hypotension. In general, they may look well particularly if they are early in their disease or very unwell if they are late in the course. On the neurologic examination, we look for focal neurological signs and papillodema. We will look for rashes, particularly for purpura. On examination, we also look for any signs of meningio irritation. There are a few of them available. The first one is kernic sign. This is when the patient's knee and hip are bent at 90 degrees. An extension of the knee is painful. Ritzinski sign, in which when the patient's neck is flexed, they lift their legs involuntarily. Nucleurigidity, which the patients have difficulty flexing their neck. Jolt accentuation, in which moving the patient's neck quickly or jolting, increases the patient's discomfort. All of these tests from meningio irritation have low sensitivity and high specificity. That means that if your patient has it, that is much more likely that they have meningitis. But if they do not have it, it does not mean they don't have the disease. For physical examination of patients with encephalitis, they will not have any signs of meningio irritation. They may have a fever, a headache, have change in level of consciousness, or presents in a seizure. They may have cold sores, this suggests herpes and Plexivirus. In summary, we talk about the pathophysiology and the history and physical impatience with meningitis and encephalitis. In the next video, we will discuss the treatment and investigations. Thank you for watching.