Infectious Diseases Abstract Infectious diseases can occur anywhere within the central nervous system (CNS). They may be caused by bacteria, virus, fungus, or parasites and may be introduced into the body by various methods, including injury, surgery, insects, or other infections. CNS infections may result in mild symptoms or critical illness. The appropriate treatment varies by the type and location of the infection, and it is further subject to other patient comorbidities. Early recognition and intervention are critical in treating patients with infectious diseases of the CNS. Keywords: abscess, encephalitis, meningitis, neurocysticercosis, prion disease, shunt infection The central nervous system (CNS) is vulnerable to many infectious diseases. Meningitis, encephalitis, and abscesses are all examples of infections of the CNS that can be caused by various bacterial, viral, or fungal pathogens. Infectious diseases may be community-acquired or nosocomial. Nosocomial infections are infections acquired during hospitalization. Common examples include pneumonia, urinary tract infections, or postoperative wound infections. Most nosocomial infections occur in critical care units. Although infections of the CNS can occur in patients who have had neurosurgical procedures, most do not warrant neurosurgical treatment. Instead, these infections are treated by infectious disease specialists. Meningitis is inflammation of the meninges (▶ Fig. 10.1). It can be caused by bacteria, a virus, or fungus. Bacterial or viral meningitis are the most common types. Fig. 10.1 Meningitis. Caused by a bacterial pathogen (Box 10.1 Common Bacterial Pathogens) Commonly affects very young or very old individuals Morbidity is variable and dependent on the specific pathogen Diabetic patients are more susceptible to bacterial meningitis Prognosis is good if treated, poor if untreated (Box 10.2 Mortality Rate of Bacterial Meningitis) Box 10.1 Common Bacterial Pathogens Community-acquired Streptococcus pneumoniae Neisseria meningitidis Haemophilus influenzae Listeria monocytogenes Nosocomial Staphylococcus aureus Pseudomonas aeruginosa Staphylococcus species Other gram-negative bacteria Box 10.2 Mortality Rate of Bacterial Meningitis More than 70% of persons who contract bacterial meningitis will die if the disease is not treated Caused by a viral pathogen (Box 10.3 Common Viral Pathogens) Can affect patients of any age Incidence and type influenced by geographic region May occur as a single isolated case or can be epidemic The virus that causes acquired immune deficiency syndrome (AIDS) interferes with the immune system; resulting infections may affect many organ systems, including the central nervous system (Box 10.4 Focus on: Central Nervous System Manifestations of AIDS) Box 10.3 Common Viral Pathogens Herpes simplex 1 and 2 (HSV-1 and HSV-2), also called human herpesvirus 1 and 2 Common cold sore Genital herpes Herpes zoster , also called human herpesvirus 3 (HHV-3) Shingles Arbovirus (arthropod-borne) West Nile virus Zika virus Enterovirus Coxsackievirus Echovirus Poliomyelitis Postviral Measles Mumps Chickenpox Box 10.4 Focus on: Central Nervous System Manifestations of AIDS About 40 to 60% of all patients with AIDS will develop neurologic symptoms Most common conditions include the following: Toxoplasmosis Primary CNS lymphoma Cryptococcal abscess Progressive multifocal leukoencephalopathy Neurosyphilis Most common CNS effects of HIV infections include the following: AIDS encephalopathy AIDS dementia Cranial neuropathies Meningitis (aseptic) Caused by a fungal pathogen Most common examples are Cryptococcus and Coccidioides (regional) Involves inflammation of the meninges, the subarachnoid space, and the cerebrospinal fluid (CSF) Ventriculitis is an infection involving the ventricular system Bacteria enter the meninges by various methods. The bacteria that cause meningitis commonly travel through the CSF after trauma, after a surgical procedure, or after a lumbar puncture. However, bacteria may also reach the meninges via the following: Blood (bacteremia) Colonization of the mucosa with passage (e.g., sinus) to the submucosa Contiguous spread Dental procedures Endocarditis Meningismus, also called meningism, is the clinical manifestation of meningeal irritation. It involves the following: Nuchal rigidity (stiff neck) Kernig’s sign; see Chapter 2: Assessment Brudzinski’s sign; see Chapter 2: Assessment Headache Fever Altered level of consciousness (LOC) Seizure Rash may be present in meningococcal meningitis Chemical meningitis is inflammation of the meninges not caused by bacteria (Box 10.5 Chemical Meningitis) Box 10.5 Chemical Meningitis Chemical meningitis, also called aseptic meningitis, is an inflammation of the meninges Not caused by infection Commonly occurs after subarachnoid hemorrhage (blood in the subarachnoid space acts as the irritant) Clinical manifestations of chemical meningitis include the following: Headaches (often severe) Nausea and vomiting Meningeal signs (e.g., stiff neck, photophobia, low back pain) Fever is not a clinical manifestation of chemical meningitis Treatment options include the following: Time Support of symptoms (i.e., pain relief, antiemetics) Dexamethasone is usually helpful After a complete history is obtained and a physical assessment is performed, various laboratory studies are carried out before meningitis can be diagnosed. Lumbar puncture (LP) with CSF studies, including culture (▶ Table 10.1) Serum C-reactive protein (CRP) has high negative predictive value for bacterial meningitis Complete blood count (CBC) and erythrocyte sedimentation rate (ESR) Polymerase chain reaction (PCR) is highly predictive of enteroviral meningitis Blood cultures Procalcitonin (Box 10.6 Procalcitonin, and ▶ Table 10.2) Box 10.6 Procalcitonin Elevated procalcitonin is an early indication of inflammatory response and is highly suggestive of infection, especially in postoperative wounds High correlation between level of procalcitonin and poor prognosis Level of procalcitonin may increase within 3 to 6 hours of stimulation, and this level is detectable in blood Condition Opening pressure (cm H2O) Appearance Cells Protein (mg/dL) Glucose Cultures Normal 8–18 Clear 0–5 < 45 60% of blood glucose level No organisms Bacterial meningitis Increased Clear or cloudy > 100 Increased Decreased Bacterial pathogens Viral meningitis May be normal or increased Clear or cloudy 10–1000 Slightly increased Normal or slightly decreased Viral pathogens Level (ng/mL) Possible cause < 0.05 Normal Local inflammatory possible; systemic disease unlikely ≥ 0.05 to < 2 Systemic inflammatory response present due to infection ≥ 2 to < 10 Sepsis likely > 10 Severe sepsis or septic shock Organ dysfunction High risk of death Infectious disease consultation Antibiotics for bacterial meningitis (Box 10.7 Starting Antibiotics), antiviral medication for viral meningitis, and antifungal medication for fungal meningitis Dexamethasone has been shown to decrease mortality when administered early in the disease course (Box 10.8 Vasogenic Edema) Relief of symptoms such as pain or fever Respiratory and circulatory support may be necessary in extreme cases Antiepileptic drugs (AEDs) for seizures (Box 10.9 Antiepileptic Drugs and Antibiotics) Except in cases of meningococcal meningitis, isolation is not necessary (universal precautions suffice) Treatment guidelines are outlined by the Infectious Diseases Society of America Box 10.7 Starting Antibiotics Early treatment is imperative to ensure a good outcome As soon as bacterial meningitis is suspected, collect the appropriate specimens and send them immediately for culture and sensitivity analysis; then begin appropriate antibiotics Do not allow ancillary tests to delay initiation of antibiotics Box 10.8 Vasogenic Edema Vasogenic edema is often seen with meningitis or encephalitis Associated with increased intracranial pressure (ICP) Dexamethasone is associated with improved outcome. Box 10.9 Antiepileptic Drugs and Antibiotics Some antibiotics (e.g., phenytoin) interfere with the absorption or metabolism of some AEDs Patients with CNS infections are susceptible to seizure activity, so be sure to monitor blood levels of AED if appropriate, External ventricular drain (EVD) may be needed for patients with ventriculitis Management of increased intracranial pressure (ICP). See also Chapter 3: Principles of Intracranial Pressure Route for intrathecal antibiotics Infection rate is approximately 6% May present within 2 weeks of shunt placement Late presentation (i.e., presentation > 6 months after shunt placement) is not uncommon Staphylococcus is the most likely infectious agent General malaise Fever Nausea and vomiting Abdominal pain (if shunt is ventriculoperitoneal) May present as shunt failure Positive CSF cultures from shunt tap or EVD Removal of all components of the infected shunt plus intravenous (IV) antimicrobial therapy as appropriate Shunt should be replaced only after CSF cultures remain negative for a determined length of time If shunt cannot be removed, antibiotics should be pumped into the ventricle through a shunt reservoir or via EVD Potentially toxic No specific antibiotic has been approved by the Food and Drug Administration Should only be used in situations in which conventional IV therapy has not been effective Encephalitis is an inflammation of brain tissue. It has been known to mimic the characteristics of brain lesions and is often seen in conjunction with meningitis. Cause may be bacterial, viral (most common), fungal, or parasitic Specific pathogen is highly influenced by geographic location Viral form is the most common type found in the United States (herpes simplex) Viral pathogens are the same as for meningitis Postviral diseases such as measles, mumps, and chickenpox can also cause encephalitis Acute disseminated encephalomyelitis is an example of postinfectious or postimmunization encephalitis Symptoms depend on the type of virus but are usually the same as the symptoms for meningitis. Symptoms of encephalitis, however, are usually more pronounced than symptoms for meningitis. LOC is especially affected. Alterations in LOC/sensorium Severe headache Fever Nausea and vomiting Focal deficits, such as motor weakness, may occur Seizures Signs of increased ICP Hydrocephalus LP with CSF studies, including cultures Blood cultures CBC, CRP, ESR, PCR Magnetic resonance imaging (MRI) may show abnormalities (e.g., small hemorrhages) (▶ Table 10.4). Test Indication Nursing implication CBC WBC increase indicates body’s response to infection Watch for signs and symptoms of infection ESR Inflammation Watch for infection CRP Presence of inflammation, especially postoperative infection, somewhere in the body Watch for infection Electrolyte panel Hyponatremia, especially in the setting of cerebral edema Monitor laboratory values for hyponatremia Administer salt supplements if indicated Maintain strict intake and output, and restrict fluids if indicated Hyperglycemia may result after dexamethasone is administered Monitor glucose levels Administer insulin if indicated Report if hyperglycemia is a new finding LP Measurement of opening pressure is contraindicated in patients with suspected abscess Assist with proper positioning of patient CSF examination, including culture Assist in maintaining sterile procedure Blood culture Indicates presence of bacterial or fungal pathogens in blood (bacteremia or fungemia) Administer antibiotics as ordered May need PICC when long-term antibiotics are indicated Often seen in conjunction with CSF infections, such as meningitis or ventriculitis MRI Lesions such as neurocysticercosis, cerebral abscess, or hemorrhagic areas resulting from encephalitis Rule out other lesions as cause of neurologic symptoms EEG Identifies seizure activity Administer AEDs as ordered Follow seizure safety protocols; see also Chapter 6: Seizures Abbreviations: AEDs, antiepileptic drugs; CBC, complete blood count; CRP, C-reactive protein; CSF, cerebrospinal fluid; EEG, electroencephalogram; ESR, erythrocyte sedimentation rate; LP, lumbar puncture; MRI, magnetic resonance imaging; PICC, peripherally inserted central catheter; WBC, white blood cell count. Antiviral medications Dexamethasone Improve symptoms (e.g., pain, fever, seizure) Treatment guidelines are outlined by the Infectious Diseases Society of America Brain tissue affected by encephalitis rarely requires biopsy Shunts are often placed in this population due to the common occurrence of hydrocephalus A brain abscess is a localized infection that has migrated to the brain from another part of the body. Usually bacterial Most common causes include the following: Infection in the sinus, inner ear, or mouth Dental procedures Trauma, such as a penetrating head wound Neurosurgical procedure Endocarditis (Box 10.10 Brain Abscess in Intravenous Drug Users) Box 10.10 Brain Abscess in Intravenous Drug Users
10.1 Infectious Diseases
10.2 Meningitis
10.2.1 Bacterial
10.2.2 Viral
10.2.3 Fungal
10.2.4 Epidemiology of Meningitis
10.2.5 Clinical Manifestations
10.2.6 Diagnosis
Laboratory Studies
(cells/µL)
(> 50)
(< 50% blood glucose)
(> 50)
10.2.7 Treatment
Medical
Surgical
10.3 Shunt Infections
10.3.1 Epidemiology
10.3.2 Clinical Manifestations
10.3.3 Diagnosis
10.3.4 Treatment
Intraventricular (Intrathecal) Antibiotics
10.4 Encephalitis
10.4.1 Clinical Manifestations
10.4.2 Diagnosis
Laboratory Studies
Imaging Studies
10.4.3 Treatment
Medical
Surgical
10.5 Abscess
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