Infections, CNS
A. Abscess and focal cerebritis
1. H&P: Headache, focal deficits, altered mental status. Seizures occur in 40%. Fever, neck stiffness, vomiting, and papilledema are uncommon. Look for other infections, especially ear, nose, mouth, lung, and heart. Ask about HIV risk factors.
2. DDx: Tumor, granuloma.
3. Causes: Anaerobic streptococci are most common. Posttraumatic or surgical cases are more likely to be Staphylococcus or Enterobacteriaceae. Many abscesses are polymicrobial.
4. Tests: CT or MRI with contrast should show ring-enhancing cavity, edema, mass effect. Blood cultures, CXR, consider echocardiogram. LP is contraindicated.
5. Rx:
a. Surgery: Needle aspiration or excision of abscess, ideally before Abx initiated.
b. Abx: Treat for ≥ 6 wks. Adjust Abx on basis of abscess cultures.
1) Ear or unknown source: Ceftriaxone 2 g IV q12h (or cefotaxime 2 g IV q4-6h) + metronidazole 500 mg IV q6h. Some also use penicillin 4-5 MU IV q4-6h.
2) HIV-positive: Add coverage for toxoplasmosis; see below.
3) Post head trauma or surgery: Vancomycin 1 g IV q12h + ceftazidime 2 g IV q8h or cefepime 2 g IV q12h.
c. Steroids: Only if severely high ICP because steroids may decrease antibiotic penetration.
B. Cryptococcosis
A fungus, Cryptococcus neoformans, the most common cause of fungal meningitis. Cryptococcal meningitis may be an emergency because pts can die suddenly from high ICP.
1. H&P: HIV, immunosuppression, pigeon exposure. Headache, fever, meningeal signs, confusion, signs of high ICP. Seizures uncommon.
2. DDx: Other meningitides.
3. Tests: CSF (see p. 19). CSF India ink stain is positive in 75%. Serum and CSF cryptococcal Ag. CT/MRI usually normal.
4. Rx: Regimens vary; consider amphotericin B and flucytosine, then fluconazole. Consider serial LPs for high ICP.
C. Cysticercosis
A helminth, the pig tapeworm Taenia solium.
1. H&P: Country of origin, seizures, headache, signs of raised ICP.
2. DDx: Other parasitic dz.
3. Tests: Stool ova and parasites. Blood serology better than CSF, but slow. Consider long-bone x-ray series to look for calcified muscle cysts. CT/MRI appearance depends on stage. Chronic, inactive lesions are calcified, nonenhancing, usually at gray-white junction. Active, degenerating cysts enhance and have edema.
4. Rx: Albendazole 15 mg/kg qd for 8 d. Regimens vary; praziquantel 50 mg/kg divided tid for 12-14 d is an alternative. Consider steroids because dying cysts cause inflammation. Surgery for cyst removal or shunting is often necessary for posterior fossa or intraventricular cysts. If cysts are inactive, rx may not help. Treat seizures.
a. Macular cysts: Rule them out before albendazole (check acuity and fundi).
b. Ventricular cysts: Consider surgery.
c. ID consult is often helpful.
D. Empyema, CNS
An IMMEDIATE SURGICAL EMERGENCY. Usually see HA out of proportion to neurological deficit.
1. Brain subdural empyemas: Frequently from sinusitis or trauma. Unlike subdural blood, they are better seen on MRI than CT (restricted diffusion). Consult ENT preoperatively for sinus drainage during the same procedure. Watch for sinus thrombosis.
2. Spinal cord empyemas: Never do an LP in a pt. with fever and back pain until you have ruled out empyema with MRI.
E. Human immunodeficiency virus (HIV)
See also Infection, p. 219.
1. Incidence: 50% of HIV pts. have a CNS or PNS problem; this can be the presenting complaint.
2. Headache: Have a very low threshold for MRI + gadolinium and LP. All pts. with HA and fever should get both.
3. Focal brain sx: Consider toxoplasmosis, lymphoma, progressive multifocal leukoencephalopathy (PML), Cryptococcus, VZV encephalitis, tuberculoma, neurosyphilis, clot, bleed, bacterial abscess.
4. Nonfocal/encephalitic sx:
a. HIV dementia complex: Subcortical dementia with psychomotor slowing; often psychosis, frontal, corticospinal, or basal ganglia signs.Related posts:
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