Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.
Otherwise healthy people with classic signs of acute brain infection can usually be diagnosed promptly. The challenge is when someone has less severe brain infections, such as chronic or partially treated meningitis, encephalitis, or other rare infections.
While examining you, the doctor is looking for particular clinical signs. Altered level of consciousness with behavioral and personality changes with a high fever always alert the doctor to the possibility of a central nervous system infection. Particular signs of meningeal irritation in someone with a fever, such as neck pain or stiffness with neck flexion, or with knee extension, or involuntary flexion of both hips with neck flexion, could signify brain infection.
The doctor will perform an eye exam, looking for swelling of the main nerve of the eye and any subtle changes in the eye movement or pupil reaction. These could represent increased intracranial pressure (ICP), seen with an abscess, or advanced meningitis or encephalitis. You will also undergo a complete neurologic examination, which helps a doctor to discover any signs and problems with your nervous system.
Standard lab work and a urine specimen will be obtained. Also, a special set of cultures from blood, urine, nose, or respiratory secretions might be taken.
Imaging studies, such as a CT scan of the head with contrast (that is, a special injectable dye that enhances the view of the brain) or an MRI scan with contrast, may be performed. These diagnostic procedures help to rule out any process in your brain that increases pressure inside the brain, as well as to show any complications of meningitis.
The definitive diagnosis is usually derived from an analysis of a sample of spinal fluid. This fluid is obtained by performing a lumbar puncture, commonly known as a spinal tap. This procedure involves inserting a small needle into an area in the lower back between the vertebrae, where fluid in the spinal canal is readily accessible. The fluid sample then is sent to a lab, where analysis will determine the existence of any CNS infection, tell the difference between bacterial and other types of infection, and identify the type of the organism responsible.
Lumbar puncture, when performed in appropriate sterile way, is a very safe procedure. The needle is inserted below the ending of the spinal cord, so no neurologic complications should occur. The sample of fluid taken is small. Strict sterile technique would eliminate the possibility of infection. The most common side effects are headache and mild tenderness at the site of insertion. Lumbar puncture is not used if there is any clinical or
X-ray evidence of the increased pressure in the brain.