Step 2 CK · Neurology

CNS Infections & Neuro-oncology (Clinical)

Name: CNS Infections & Neuro-oncology (Clinical)
Creator: Veli Bakalov, MD

From empiric antibiotics and acyclovir to the ring-enhancing lesion and the cord-compression emergency

Neurology·Demyelinating, Infectious & Neoplastic Disease·4 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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Bacterial meningitis CSF: high opening pressure, neutrophils (often >1000), glucose <40 mg/dL or CSF:serum <0.4, high protein; viral = lymphocytes with normal glucose; fungal or TB = lymphocytes with low glucose.
Never delay treatment for imaging: blood cultures → antibiotics + dexamethasone → CT only for focal deficit, papilledema, seizure, immunocompromise, or depressed consciousness → LP.
Empiric adult coverage is ceftriaxone + vancomycin; add ampicillin for Listeria if over 50, pregnant, or immunocompromised; neonates get ampicillin + cefotaxime (or gentamicin).
Give dexamethasone with or before the first antibiotic dose in suspected pneumococcal meningitis to cut death and hearing loss; continue only if pneumococcus is confirmed.
Meningococcal disease: petechial or purpuric rash and Waterhouse-Friderichsen adrenal hemorrhage; close contacts get rifampin, ciprofloxacin, or ceftriaxone.
Fever, seizures, and temporal-lobe MRI changes with red cells in the CSF = HSV encephalitis; start IV acyclovir immediately, before PCR returns.
Cryptococcal meningitis (HIV, CD4 <100): India ink and CrAg positive (CrAg is more sensitive); amphotericin B + flucytosine, then fluconazole; serial LPs for high opening pressure.
Multiple ring-enhancing lesions in advanced HIV = toxoplasmosis; multiple gray-white junction lesions = metastases, the most common brain tumor (glioblastoma is the most common primary malignant, meningioma the most common benign).
Cancer patient with back pain then weakness, sensory level, or urinary retention: IV dexamethasone and emergent whole-spine MRI, then radiation or surgery.

Meningitis: recognition and the CSF

Presentation. The classic triad of bacterial meningitis is fever, nuchal rigidity, and altered mental status, often with headache and photophobia. Kernig and Brudzinski signs support meningeal irritation. Only about 40–50% of patients have the full triad, but roughly 95% have at least two of fever, neck stiffness, headache, or altered mentation. The course is rapidly progressive: treat it as an emergency.

CSF patterns by cause

Cause	Opening pressure	Cells	Glucose	Protein
Bacterial	High	Neutrophils, often >1000	Low: <40 mg/dL or CSF:serum <0.4	High
Viral	Normal or mildly high	Lymphocytes	Normal	Mildly high
Fungal or TB	High (very high in cryptococcus)	Lymphocytes	Low	High
HSV encephalitis	Normal or high	Lymphocytes plus red cells	Normal	Mildly high

Neutrophils with low glucose mean bacteria until proven otherwise.

Emergency management of bacterial meningitis

Never delay antibiotics for imaging. Get the LP promptly, but obtain a head CT FIRST when herniation risk is higher: focal deficit, papilledema, new seizure, immunocompromise, or reduced consciousness. When CT is needed, draw blood cultures and give empiric antibiotics plus dexamethasone before the scan.

Blood culturesDrawn immediately; never a reason for delay.
Empiric antibiotics + dexamethasoneCeftriaxone plus vancomycin, with ampicillin when indicated.
Head CT if red flagsFocal deficit, papilledema, seizure, immunocompromise, depressed consciousness.
LP and CSF studiesGram stain, culture, cell count, glucose, protein.

Emergency meningitis pathway

Empiric coverage by patient group

Group	Likely organisms	Empiric regimen
Neonates	Group B strep, E. coli, Listeria	Ampicillin + cefotaxime (or gentamicin)
Adults	S. pneumoniae (including resistant strains), N. meningitidis	Ceftriaxone + vancomycin
Age >50, pregnant, or immunocompromised	Add Listeria monocytogenes	Ceftriaxone + vancomycin + ampicillin
After neurosurgery or with a shunt	Staphylococci, gram-negative rods including Pseudomonas	Vancomycin + cefepime (or meropenem)

Dexamethasone. Give it with or just before the first antibiotic dose in suspected pneumococcal meningitis; it reduces mortality and neurologic sequelae, including hearing loss. Continue it only if pneumococcus is confirmed.

Steroids blunt the inflammatory burst from bacterial lysis, so giving them after antibiotics loses the benefit.

Meningococcus. Neisseria meningitidis causes a petechial or purpuric rash and can cause Waterhouse-Friderichsen syndrome (adrenal hemorrhage with shock). Place the patient on droplet precautions for the first 24 hours of therapy. Close contacts (household members, roommates, anyone exposed to oral secretions) receive prophylaxis with rifampin, ciprofloxacin, or a single dose of ceftriaxone; ceftriaxone is preferred in pregnancy.

Encephalitis, cryptococcus, and ring-enhancing lesions

HSV-1 encephalitis. Fever, altered mentation, seizures, and personality change. MRI shows temporal lobe edema or hemorrhage; CSF shows lymphocytes and red cells, and HSV PCR confirms. Start IV acyclovir empirically at once and do not wait for the PCR: untreated disease carries roughly 70% mortality. Keep the patient hydrated, because acyclovir can crystallize in the renal tubules.

Cryptococcal meningitis. Subacute headache and fever in HIV with CD4 under 100. India ink and serum or CSF cryptococcal antigen (CrAg) are positive; CrAg is far more sensitive than India ink, so a negative India ink does not exclude the diagnosis. Induction is amphotericin B plus flucytosine, then fluconazole; treat high opening pressure with serial LPs. Antiretroviral therapy is deferred for several weeks to limit immune reconstitution inflammatory syndrome.

Brain abscess. A ring-enhancing lesion with surrounding edema, spread from otitis, sinusitis, or dental infection or seeded hematogenously; it is often polymicrobial (streptococci, anaerobes). Treat with aspiration or drainage plus antibiotics, and avoid LP because of herniation risk.

Toxoplasmosis: multiple ring-enhancing lesions in advanced HIV (CD4 under 100); treat empirically with pyrimethamine and sulfadiazine (with leucovorin) and biopsy if there is no response.
Glioblastoma and metastasis: the main neoplastic causes of a ring-enhancing mass.
Primary CNS lymphoma: the key HIV alternative when a lesion fails to respond to toxoplasma therapy.

Brain tumors and raised intracranial pressure

Red flags. Progressive headache that is worse in the morning, with Valsalva, or when lying down; a new-onset seizure in an adult; a focal deficit; or signs of raised ICP (papilledema, vomiting). Get a contrast MRI.

A first unprovoked seizure in an adult mandates neuroimaging to exclude a mass.

Metastases outnumber primaries. Metastases are the most common brain tumors, appearing as multiple lesions at the gray-white junction; primaries include lung (most common), breast, melanoma, renal, and colon cancer. Glioblastoma is the most common primary malignant tumor (an irregular ring-enhancing mass that can cross the corpus callosum); meningioma is the most common benign tumor (a dural-based, extra-axial mass).

Raised ICP from a tumor. Elevate the head of the bed, give dexamethasone for vasogenic edema, use mannitol or hypertonic saline, and use brief hyperventilation only as a bridge. Avoid LP when a mass with edema is present because of herniation risk.

Malignant spinal cord compression

Back pain first, then deficits. Progressive back pain, worse at night or when recumbent, is followed by weakness, a sensory level, and bowel or bladder dysfunction. Common primaries are prostate, breast, and lung cancer, and the thoracic spine is the most frequent site.

Management. Give dexamethasone immediately and obtain urgent whole-spine MRI (other levels may be involved), then proceed to radiation or surgical decompression.

Function at presentation predicts recovery, so treat ambulatory patients before they lose motor function; never wait for weakness to image a cancer patient with new back pain.