Chapter 148. Central Nervous System and Spinal Infections

Clinical Features

In classic and fulminant cases of bacterial meningitis, the patient presents with fever, headache, neck stiffness, and altered mental status. Seizures may occur in up to 25% of cases. The presenting picture, however, may be more nonspecific, particularly in the very young and elderly. It is important to inquire about recent antibiotic use, which may cloud the clinical picture in a less florid case. Other key historical data include living conditions (eg, Army barracks, college dormitories), trauma, immunocompetence, immunization status, and recent neurosurgical procedures.

Physical examination should include assessment for meningeal irritation with resistance to passive neck flexion, Brudzinski sign (flexion of hips and knees in response to passive neck flexion), and Kernig sign (contraction of hamstrings in response to knee extension while hip is flexed). Examine the skin for the purpuric rash characteristic of meningococcemia or streptococcemia. Percuss the paranasal sinuses and examine the ears for evidence of primary infection in those sites. Assess for focal neurologic deficits and check the fundi for papilledema, which indicate increased intracranial pressure.

Diagnosis and Differential

When the diagnosis of bacterial meningitis is entertained, treatment should precede diagnostic testing (see ED Care and Disposition Section). Performing a lumbar puncture (LP) is mandatory when bacterial meningitis is suspected. At a minimum, analyze cerebrospinal fluid (CSF) for gram stain and culture, cell count, protein, and glucose. Typical CSF results for meningeal processes are listed in Table 148-1. Additional studies to be considered are latex agglutination or counterimmune electrophoresis for bacterial antigens in potentially partially treated bacterial cases, India ink or serum cryptococcal antigen in immunocompromised patients, acid-fast stain and culture for mycobacteria in tuberculous meningitis, Borrelia antibodies for possible Lyme disease, and viral cultures in suspected viral meningitis. Other laboratory tests should include a complete blood count, blood cultures, coagulation studies, and basic metabolic panel.

Table 148-2 lists suggested criteria for obtaining head CT prior to LP. In these cases, administer empiric antibiotic therapy before patient transport to CT.

The differential diagnosis includes subarachnoid hemorrhage, meningeal neoplasm, brain abscess, viral encephalitis, cerebral toxoplasmosis, and other infectious meningitides.

Emergency Department Care and Disposition

1. Emergent respiratory and hemodynamic support is given top priority.

2. Upon presentation of the patient with suspected bacterial meningitis, always administer empiric antibiotic therapy as soon as possible and never delay it for neuroimaging or LP. Empiric treatment for bacterial meningitis is based on the likelihood of certain pathogens and risk factors (Table 148-3).

3. Dexamethasone (10 milligrams IV in adults, 0.15 milligram/kilogram IV in children) before or at the time of first antibiotic administration has been shown to be beneficial in improving outcomes in bacterial (Streptococcus Pneumoniae) meningitis.

4. Avoid hypotonic fluids. Monitor serum sodium levels in order to detect the syndrome of inappropriate antidiuretic hormone or cerebral salt-wasting.

5. Manage potential complications of meningitis, seizures, hyperpyrexia, increased intracranial pressure, coagulopathy, and systemic consequences of a comatose state, with standard methods.

6. Manage viral meningitis, without evidence of encephalitis, on an outpatient basis as long as the patient is nontoxic in appearance, can tolerate oral fluids, and has reliable follow-up within 24 hours. However, it remains a diagnosis of exclusion; unless the diagnosis of viral meningitis is obvious, admission is warranted.

Clinical Features

Viral encephalitis is a viral infection of brain parenchyma producing an inflammatory response. It is distinct from, although often coexists with, viral meningitis. In North America, viruses that cause encephalitis are the arboviruses (including the West Nile virus), herpes simplex virus (HSV), herpes zoster virus (HZV), Epstein-Barr virus, cytomegalovirus (CMV), and rabies.

Encephalitis should be considered in patients presenting with any or all of the following features: new psychiatric symptoms, cognitive deficits (aphasia, amnestic syndrome, acute confusional state), seizures, and movement disorders. Headache, photophobia, fever, and meningeal irritation may be present. Assessment for neurologic findings and cognitive deficits is crucial. Motor and sensory deficits are not typical. Encephalitides may show special regional trophism. HSV involves limbic structures of the temporal and frontal lobes, with prominent psychiatric features, memory disturbance, and aphasia. Some arboviruses predominantly affect the basal ganglia, causing chorea-athetosis and Parkinsonism. Involvement of the brainstem nuclei leads to hydrophobic choking characteristic of rabies encephalitis.

Symptoms of West Nile virus infection include fever, headache, muscle weakness, and lymphadenopathy. Most infections are mild and last only a few days. More severe symptoms and signs consist of high fever, neck stiffness, altered mental status, tremors, and seizures. In rare cases (mostly involving the elderly), the infection can lead to encephalitis and death.

Diagnosis and Differential

Findings on CT or magnetic resonance imaging (MRI) and LP aid in the ED diagnosis of encephalitis. Neuroimaging, particularly MRI, not only excludes other potential lesions, such as brain abscess, but may display findings highly suggestive of HSV encephalitis if the medial temporal and inferior frontal gray matter is involved. Findings of aseptic meningitis are typically found on CSF examination. For the West Nile virus, the most widely used screening test is the IgM ELISA assay for detecting acute antibody.

The differential diagnosis includes brain abscess; Lyme disease; subacute subarachnoid hemorrhage; bacterial, tuberculous, fungal, or neoplastic meningitis; bacterial endocarditis; postinfectious encephalomyelitis; toxic or metabolic encephalopathies; and primary psychiatric disorders.

Emergency Department Care and Disposition

1. Admit the patient suspected of suffering from viral encephalitis. Treat patients with suspected HSV or HZV encephalitis with acyclovir 10 milligrams/kilogram IV every 8 hours. Treat patients with suspected CMV encephalitis with ganciclovir 5 milligrams/kilogram IV every 12 hours.

2. Manage potential complications of encephalitis—seizures, disorders of sodium metabolism, increased intracranial pressure, and systemic consequences of a comatose state—with standard methods.

3. There is no specific treatment for the West Nile virus infection. In more severe cases, intensive supportive therapy is indicated. The primary prevention step is advocating the use of insect repellant containing DEET when people go outdoors during dawn or dusk.

Clinical Features

A brain abscess, which is a focal pyogenic infection, is composed of a central pus-filled cavity, ringed by a layer of granulation tissue and an outer fibrous capsule. Since patients typically are not acutely toxic, the presenting features of brain abscess are nonspecific. Presenting signs and symptoms include headache, neck stiffness, fever, vomiting, confusion, or obtundation. The presentation may be dominated by the origin of the infection (eg, ear or sinus pain). Meningeal signs and focal neurologic findings, such as hemiparesis, seizures, and papilledema, are present in less than half the cases.

Diagnosis and Differential

Brain abscess can be diagnosed by a CT scan of the head with contrast, which demonstrates one or several thin, smoothly contoured rings of enhancement surrounding a low-density center and in turn surrounded by white matter edema. LP is contraindicated if brain abscess is suspected or after the diagnosis has been established. Routine laboratory studies are usually nonspecific. Blood cultures should be obtained.

The differential diagnosis includes cerebrovascular disease, meningitis, brain neoplasm, subacute cerebral hemorrhage, and other focal brain infections, such as toxoplasmosis.

Emergency Department Care and Disposition

1. Decisions on antibiotic therapy for brain abscess are dependent on the likely source of the infection (Table 148-4).

2. Neurosurgical consultation and admission are warranted since many cases will require surgery for diagnosis, bacteriology and, definitive treatment.