brain, spinal cord, and nerve disorders
Introduction to Meningitis
Diagnosis of Meningitis
Spinal tap and analysis of cerebrospinal fluid Doctors often suspect meningitis based on symptoms. But because meningitis can be serious, tests are done. If doctors suspect bacterial meningitis, they first take a sample of blood to test and culture (to grow microorganisms) to determine whether bacteria are present, and, if so, to identify them. However, bacterial meningitis cannot be diagnosed by blood tests. For all types of meningitis, doctors do a Spinal Tap (lumbar puncture) to confirm the diagnosis and identify the cause. The sample of cerebrospinal fluid is withdrawn and sent to a laboratory to be examined, analyzed, and cultured. During a spinal tap, a thin needle is inserted between two bones (vertebrae) in the lower spine to withdraw cerebrospinal fluid. Then the following are done: Close examination of the cerebrospinal fluid: The fluid is normally clear but may be cloudy in people with meningitis. Measurement of the pressure in the subarachnoid space (which contains the cerebrospinal fluid) before the cerebrospinal fluid is withdrawn: Pressure is usually high in meningitis. Analysis of cerebrospinal fluid in a laboratory: Sugar and protein levels and the number and type of white blood cells in the fluid are determined. This information helps doctors diagnose meningitis and distinguish between bacterial and viral meningitis. Examination of cerebrospinal fluid under a microscope to check for and identify bacteria. A special stain (called Gram stain) is used to show the bacteria more clearly and to help identify them. Other tests However, if they suspect that pressure within the skull is greatly increased (for example, by an abscess, tumor, or another mass in the brain), computed tomography (CT) or magnetic resonance imaging (MRI) may be done first to check for such masses. Doing a spinal tap when pressure within the skull is increased may be dangerous. Parts of the brain may shift downward. If these parts are pressed through the small openings in the tissues that separate the brain into compartments, a life-threatening disorder called Herniation: The Brain Under Pressure results. If a spinal tap cannot be done right away and doctors suspect bacterial meningitis, doctors begin treatment with antibiotics without waiting for test results. After pressure within the skull is lowered or if no mass is detected, a spinal tap is done, and doctors adjust treatment, if needed, after they get the results. 