Meningitis

Meningitis is inflammation of the meninges and subarachnoid space. It usually results from infections, but it may also result from other disorders or reactions to drugs. Meningitis is classified to:

 ►bacterial meningitis (caused by bacterial infection) and 

 ►aseptic meningitis (when the meningeal inflammation is not caused by bacteria-causes of aseptic meningitis include viral infections, other miscellaneous infections such as coccidioidomycosis, leptospirosis, toxoplasmosis, malaria, and  non-infectious conditions such as sarcoidosis, brain tumors, metastases of cancer to the meninges and some drugs, such as trimethoprim-sulfamethoxazole, ibuprofen, and carbamazepine.)

Acute bacterial meningitis is an infectious emergency because it is a rapidly progressive and serious disease. In adult persons, the most common cause of community-acquired meningitis is Streptococcus pneumoniae. Other common causes are Neisseria meningitidis, Listeria monocytogenes, Streptococci, Staphylococcus aureus, Haemophilus influenzae, and Gram-negative bacilli.

Clinical Presentation of meningitis

Fever, headache, and nuchal rigidity (neck stiffness) are present in most cases of meningitis.

Some patients may manifest a change in mental status (with the patient appearing lethargic or obtunded) and/or seizures.

In meningococcemia (due to severe infection by Neisseria meningitidis )a characteristic petechial rash is seen.

Physical examination may reveal signs of meningeal
irritation which include: 

►Difficulty touching the chin to the chest with the mouth closed

►Brudzinski’s sign (passive flexion of the neck results in spontaneous flexion of the hips and knees)

►Kernig’s sign (passive extension of the knee while the hip is flexed elicits pain in the back) 

Diagnostic tests in meningitis 

In a case with any suspicion of meningitis lumbar puncture should usually be performed. Lumbar puncture is contraindicated if there is a bleeding disorder. 

Before lumbar puncture, computed tomography (CT) of the brain is indicated in suspected meningitis in patients with the following characteristics: patient age >60 years, immunocompromise, new- onset seizures, papilledema, altered consciousness, or focal neurologic deficits.

Typical characteristics of CSF in bacterial meningitis:
cell count of 1,000-5,000/ microliter and glucose level <40 mg/ dL
In bacterial meningitis, the differential blood cell count usually shows a high proportion of neutrophils

Treatment of meningitis

If patients appear ill and findings suggest meningitis, intravenous bactericidal antibiotics that can cross the blood-brain barrier and corticosteroids (dexamethasone to reduce cerebral edema and cranial nerve inflammation) are started as soon as blood cultures are drawn and even before lumbar puncture. Also, if lumbar puncture is delayed pending brain CT results, antibiotic and corticosteroids administration begins before neuroimaging.
Empirical antibiotic therapy for bacterial meningitis:
In neonates cefepime plus ampicillin
In patients with age 1 month - 50 years: Vancomycin plus a
third-generation cephalosporin (ceftriaxone or cefotaxime)
In patients with age> 50 years: Ampicillin, plus vancomycin, plus a third-generation cephalosporin
In patients post a neurosurgical operation or with penetrating head trauma, or a CSF shunt: Vancomycin plus cefepime, ceftazidime, or meropenem.

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Bibliography 

Overview of Meningitis-MSD professional manual

Meningitis-Clinical Advisor-decision support in medicine

van de Beek D, Cabellos C, Dzupova O, et al. ESCMID guideline: diagnosis and treatment of acute bacterial meningitis.Clin Microbiol Infect. 2016;22 Suppl 3:S37-62.
LINK https://linkinghub.elsevier.com/retrieve/pii/S1198-743X(16)00020-3

van Ettekoven CN, van de Beek D1, Brouwer MC. Update on community-acquired bacterial meningitis: guidance and challenges.Clin Microbiol Infect. 2017;23(9):601-606. doi: 10.1016/j.cmi.2017.04.019
LINK Update on community-acquired bacterial meningitis: guidance and challenges

Lin, AL, Safdieh, JE. The evaluation and management of bacterial meningitis: current practice and emerging developments. Neurologist. 2010;16:143-151.