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t lnfectious Disease Brain Abscess Diagnosis Brain abscess may occur from hematogenous spread, from an ENT source, from penetrating trauma, or after neurosurgery. Clinical presentation typically includes severe headache; fever and neck stiffness may not always be present. Testing MRI of the CNS is the cornerstone of diagnosis. Aspiration of the brain abscess for culture is preferred for definitive diagnosis. Treatment Empiric antimicrobial treatment should be based on the suspected source and Gram stain results. If a predisposing condition is unknown, select empiric IV vancomycin plus metronidazole and a third-generation cephalosporin. A narrowed regimen is based on culture results. Abscesses >2.5 cm should be excised or drained stereotactically. DON'T BE TRICKED . LP is contraindicated in patients with brain abscess because ofthe potential for increased intracranial pressure and risk for herniation. Herpes Simplex Encephalitis Diagnosis Infection with HSV 1 is the most common cause of sporadic encephalitis in the United States. Fever, altered mental status, headache, seizure, and focal neurologic deficits suggest HSE. Testing CSF testing shows lymphocytic pleocytosis and, when necrosis is extensive, erythrorytes. HSV PCR of the CSF allows rapid diagnosis of HSE. Temporal lobe abnormalities on imaging and periodic lateralizing epileptiform discharges on EEG suggest HSE. DO]I'T BE TRIGKED o Order HSV PCR in all suspected cases ofencephalitis, even ifnot typical for HSV encephalitis. o Do not order CSF culture for HSV or serologic testing for HSV. Treatment High dose IV acyclovir should be started within 24 hours of symptom onset and continued for 14 to 21 days. West Nile Neuroinvasive Disease Diagnosis Mosquitoes serve as the primary vector, and most human infections occur during the summer and early fall. WNND may present with meningitis, encephalitis, or myelitis. Older adults and immunocompromised patients are at highest risk. 222

lnfectious Disease Severe disease may manifest as acute asymmetric flaccid paralysis. Diagnosis is established by detecting IgM antibody to WNV in the serum and CSE Treatment Treatment is Iimited to supportive care. Skin and Soft Tissue lnfection Diagnosis Most diagnoses are based on clinical findings alone. Choose blood cultures in the presence of sigrrs and symptoms of systemic toxicity. STUDY TABLE: Skin and Soft Tissue lnfection lf you see.. Think.. Brightly erythematous skin lesion, often on face, with very distinct elevated Erysipelas borders lnfection involving the deeper dermis and subcutaneous fat tissue, often on Cellulitis legs; borders less distinctthan erysipelas Honey-colored, crusted pustules lmpetigo caused by p-hemolytic Streptococcus or Staphylococcus Sepsis, cellulitis, and hemorrhagic bullae after exposure to saltwater fish or Vi b ri o vu I nifi cus i nfeclion shellfish in patients with cirrhosis Chronic nodular infection of distal extremities with exposure to fish tanks or Mycobacterium marinum marine environments Chronic nodular infection of distal extremities with exposure to plants/soil Sporotrichosis Sepsis following a dog bite in a patient with asplenia Ca pnocyto pha g a ca ni m o rsu s Swelling and erythema with pain out o{ proportion to physical examination Necrotizing (deep) soft tissue infection (surgical findings emergency) Acute, tender, well-delineated, purulent papular lesions Abscess cause d by Sta phyl ococcu s a u re u s Follicle-centered pustules in the beard and pubic areas, axillae, and thighs S. aureus folliculitis Follicle-centered erythematous papules and pustules on the trunk, axillae, Pse udomon as t ollicu litis and buttocks after hottub or whirlpool exposure Cellulitls: Cellulitis is characterized by demarcated areas of tender erythema 223