Brain Mass, Abscess (Approach to fever/headache)

1. Approach to the immunocompromised pt with HA, fever, confusion:
--always think CNS pathology, even if there are no focal neurologic deficits; only 50% of these patients even mount a fever in the setting of a brain abscess.  Focal sxs are usually a late manifestation.  Often times HA is the only symptom, and if you are not thinking about infection, you may miss it
--LP is often non-diagnostic in brain abscesses.  Unless the abscess has ruptured, you may get a picture of aseptic meningitis (wbcs, but no organisms, no significant derangement in glucose or protein).  You do want to do an LP, but it does not rule out an abscess.  Mainly you are looking for signs of malignancy and concomitant meningitis.
--regarding LP, it is safe to LP before doing a CT if there are no signs of increased ICP (ie. no papilledema or focal neuro sxs).  However, we often doubt our PE skills when it comes to papilledema.  When it doubt, it is ok to get the CT first, but DO NOT delay empiric abx treatment.
--MRI is more sensitive than CT for brain abscesses, malignancy, but again, should not delay treatment.

2. DDx of a brain mass:
--malignancy is always on the differential, esp in pts with known cancer.  It is often hard to distinguish from infection based on imaging.  More likely in certain malignancies (ie. lymphoma), which have a predilection for the CNS.  This particular pt did have several neg LPs for malignant cells during his induction cycle
--hemorrhage/infarct (bright on a non-con; LP may have RBCs)
--abscess: usually fungal vs. bacterial. Fungal is more common in immune compromised pts than normal hosts.  Wide differential, including anaerobes (usually via direct spread from sinuses, teeth, lungs), aerobes (staph, strep--more common after a neurosurgical procedure or via embolization from other source, ie . endocarditis), nocardia, toxoplasma, listeria and fungi (cocci, crypto, aspergillus, candida, mucormycoses)

3. Empiric tx of suspected brain abscess:
--cover broadly, with particular attention to the clinical history.  In this patient, he was at risk for bacterial abscesses b/c of his poor dentition, with possible maxillary sinus extension.  He also had risk for soil-related fungi, such as scedosporium and aspergillus. 
--broad spectrum abx for g-/g+ bacteria (ie. 4th gen ceph or carbapenem +/- vancomycin)
--if any concern for concomitant encephalitis, cover the appropriate viruses as well (HSV; CMV and HHV-6 in a transplant patient). 
--remember, voriconazole covers most fungi, including aspergillus and scedosporium but NOT mucor. 
--Ampho covers most fungi, including mucor, but the lipid formulations have variable CSF penetration.
--echinocandins are really only appropriate for candida species, and maybe for synergy
--fluconazole has a limited spectrum and significant resistance patterns--should not be used for empiric therapy (posaconazole and itraconazole should not be used empirically as they are po and have poor CSF penetration)
--TMP-SMX covers nocardia and toxoplasma

(Victoria Kelly MD, 6/15/10)