Book- Based Pathophysiology Analysis: Meningitis is an inflammation of the protective layers surrounding the brain and spinal cord, known as the meninges. It is more common in young children and people under 20, and can be caused by either bacterial or viral infections. Risk factors include skipping immunizations, being in a crowded community setting, and having a compromised immune system, upper respiratory tract infection or other infections in the head. Bacterial meningitis is often caused by Streptococcus Pneumoniae or Neisseria meningitidis, while viral meningitis can be caused by enterovirus, herpes virus, mumps virus, or HIV. The infection can occur as a result of a primary infection, such as otitis media, sinusitis, or mastoiditis, or from neurosurgical operations, head trauma or anatomic deformities that allow the infective organisms to enter the meninges. Once the infective microorganism enters the body, it invades the bloodstream and triggers an immune response which causes inflammation as the body's natural defense against infection. The organism then spreads to the central nervous system through the bloodstream. This causes the blood vessels to dilate and increase in capillary permeability, leading to leakage of plasma proteins and other blood components into the surrounding tissue, forming petechiae. The blood-brain barrier also becomes permeable, allowing for leakage of water, proteins, white blood cells, and infective organisms into the subarachnoid space, where they proliferate in the cerebrospinal fluid. This leads to an increase in bacteria, white blood cells/neutrophils, and protein in the diagnostic test, as well as a decrease in glucose in the cerebrospinal fluid as the bacteria uses it as a source of energy. The presence of bacteria in the subarachnoid space causes an inflammatory response which leads to the inflammation of the leptomeninges, the protective layers surrounding the brain and spinal cord. This results in meningeal irritation and causes pain sensitive dura mater to be irritated. This can lead to symptoms such as headache, stiff neck, sore back, and seizures. Two common signs of meningitis are the Kernig sign and the Brudzinski sign. The Kernig sign is positive when a person in a lying position with a flexed knee is unable to extend the leg and experiences pain. The Brudzinski sign is positive when flexing the neck causes irritation and excites the nerve roots involving the hip and knee flexors, causing flexion of the knees and hips. The inflammation caused by meningitis can affect the normal function of the central nervous system, including the cranial nerve II (optic nerve), leading to sensitivity to light (photophobia). Additionally, fever and weakness occur as a result of the inflammation increasing the basal metabolic rate. Fever is also an indication of an ongoing infection in the individual. An increase in fever can cause an increase in the workload of the heart, leading to tachycardia. If the heart is unable to keep up with the increased workload, the lungs will compensate by increasing the respiratory rate. Overall, this is the process by which meningitis affects the body's physiology.
