Neurological Infections PDF

NEUROLOGICAL INFECTIONS DR. TERESA WANG LEARNING OBJECTIVES 1. Understand that infections of the central nervous system is a medical emergency 2. Know the different types of CNS infections 3. Appreciate the different routes of acquiring CNS infections 4. Describe the principles in interpreting t...

NEUROLOGICAL INFECTIONS DR. TERESA WANG LEARNING OBJECTIVES 1. Understand that infections of the central nervous system is a medical emergency 2. Know the different types of CNS infections 3. Appreciate the different routes of acquiring CNS infections 4. Describe the principles in interpreting the CSF findings in meningitis/meningoencephalitis 5. Know the principle of treatment for meningitis/meningoencephalitis ANATOMY OF NEUROLOGICAL SYSTEM • Central nervous system (CNS) • Brain • Spinal cord • Peripheral nervous system (PNS) • Peripheral nerves Meninges + Brain parenchyma Subarachnoid space IMPORTANT MESSAGE • Infection involving CNS is one of the few medical emergencies relating to infectious diseases • Often life-threatening and can have severe sequelae • • • • Coma Decreased mental capacity Seizure, evolving to epilepsy Persistent neurological deficit TYPES OF INFECTIONS Name Definition Meningitis Infection within subarachnoid space and/or throughout the leptomeninges Encephalitis Inflammation of brain parenchyma Meningoencephalitis Concomitant meningitis with encephalitis Brain abscess Localized collections of pus in brain ROUTES OF INFECTION Haematogenous spread Through choroid plexus or other blood vessels of brain to subarachnoid space *The most common route of CNS infections Direct spread from adjacent infected site Otitis media Sinusitis Mastoiditis Anatomic defects allowing microbes to get access to CNS Surgery Trauma Congenital abnormalities Travel along nerves to the brain Rabies HSV *The least common route of CNS infection MENINGITIS CLINICAL PRESENTATION • Fever • Headache • Neck stiffness • Altered mental status • Photophobia • Vomiting • Seizure • Focal neurological deficits • Disseminated disease due to causative agents CLINICAL PRESENTATION • Depending on: • Speed of onset of initial presentation • Rate of progression of the illness • CSF findings • Classified into: • • Acute (progress in hours to days) Subacute or chronic (progress in days to weeks) Types of meningitis Causative agents CSF finding Opening pressure (mmH2O) Normal Nil WBC/mm3 Predominant cell type Protein (mg/dL) Glucose (CSF/Blood ratio) <200 0-5 None 15-50 >0.6 Acute (Refer to bacterial next table) Increased 5-20,000 (mean 800) PMN >100 <0.6 Acute viral Enteroviruses HSV-2 VZV Arbovirus Mumps Slight increase 2-2000 (mean 80) Lym 50-100 or normal Normal Subacute MTB /chronic Cryptococcus Histoplasma Coccidioides Increased 5-2000 (mean 100) Lym >50 <0.6 DIAGNOSIS • Lumbar puncture to get CSF • • • • Opening pressure Cell count Protein Glucose • Gram stain, India ink test • Polymerase chain reaction (PCR) assay • Antigen detection assay • Serologic tests for specific antibody • Culture Gram stain of N. meningitidis in CSF with associated PMNs. N. meningitidis may occur intracellularly or extracellularly in PMN leukocytes and will appear as gram-negative, coffee-bean shaped diplococci. Purpura fulminans caused by N. meningitidis Gram stain of S. pneumoniae with WBCs. S. pneumoniae may occur intracellularly or extracellularly and will appear as gram-positive diplococci, sometimes occurring in short chains. India ink preparation for Cryptococcus spp. The presence of capsules will produce a halo around the yeast cells against the dark background. TREATMENT • Empirical treatment should be started immediately after collection of CSF • Antibiotics of choice: • Good penetration into CSF • Bactericidal • Prolonged course (at least 2 weeks) PREVENTION • Vaccination • S. pneumoniae • H. influenzae • N. meningitidis • Chemoprophylaxis • Group B streptococcuscarrying pregnant women ENCEPHALITIS CLINICAL PRESENTATION • • • Fever • • • Seizures Headache Altered mental status Focal neurologic deficits Coma CAUSATIVE AGENTS Predisposing factors Organisms Neonate HSV-2 Child over age of 1 year and adult HSV-1 VZV Mosquito bites Japanese encephalitis Animal bites (dog, cat, bat, raccoon) Rabies Travelling history Arboviruses (West Nile virus, Eastern and Western equine encephalitis) Post-infection/immunization encephalitis VZV Measles Influenza DIAGNOSIS • CSF • Cell count, protein and glucose may all be normal • PCR-based testing to look for viral agents • Viral-specific antibody • • Imaging esp. MRI • Rabies: EEG • PCR of CSF/saliva/brain tissue • Nuchal biopsy with fluorescent antibody staining TREATMENT • Supportive • If available, antiviral agents targeting the causative agents • Acyclovir • Oseltamivir - VZV, HSV - Influenza PREVENTION • Targeted population and Pathogens-specific • E.g. • Pre- and post-exposure vaccination against rabies • Caesarian section for pregnant women with active HSV lesions BRAIN ABSCESS CLINICAL PRESENTATION • • • • • Headache Fever Behavioural changes Focal neurological deficits Seizures • • • Papilloedema Nausea Vomiting Bacteria Otitis media or sinusitis S. pneumoniae, anaerobic streptococci, gramnegative anaerobes such as Bacteroides, Prevotella and Fusobacterium Dental infection Viridans streptococci, anaerobic streptococci, gramnegative anaerobes, Actinomyces Trauma or neurosurgery S. aureus, S. epidermidis, aerobic and anaerobic streptococci Neutropenia Aerobic gram-negative rods (Enterobacteriaceae) HIV Listeria, Nocardia, Mycobacterium Endocarditis S. aureus, viridans streptococci Fungi Immunocompromised Moulds (Aspergillus, Mucor, Rhizopus), Cryptococcus Parasites HIV Toxoplasma gondii Ingestion of feacescontaminated raw vegetables Cysticercosis by cysts of Taenia solium DIAGNOSIS • Lumbar puncture is absolutely contraindicated • Imaging • CT brain or MRI brain for any rim-enhancing lesions in brain parenchyma • Drained pus for microscopy and culture • Serology MRI brain of a 40-year-old man with brain abscess caused by Streptococcus salivarius. The image shows hypointense lesions in the region of occipital lobe. MRI brain of a 24-year-old man with HIV infection. The image shows hypointense lesions in the region of the thalami (arrows) caused by toxoplasmosis. TREATMENT • Surgical drainage is usually needed • Reduce bacterial load in the lesion • Difficult for antimicrobial agents to penetrate into the abscess • High acidity inside the abscess may render the antimicrobial agents ineffective • Appropriate antimicrobial agents SUMMARY 1. CNS infection is a serious infection and a medical emergency that needs to be managed promptly. 2. CNS infections include meningitis, encephalitis, meningoencephalitis and brain abscess. 3. People may acquire CNS infections by haematogenous spread, direct spread from adjacent infections sites, access from anatomic defects in the CNS, and retrograde spread from peripheral nerves. 4. The differential white cell counts, the protein and glucose level in CSF provide clues on the possible cause for meningitis/meningoencephalitis. 5. Empirical antimicrobial agents should be started once CSF has been collected for investigations in cases of meningitis/meningoencephalitis. REFERENCES • Levinson W. Review of Medical Microbiology and Immunology. 14th edition. McGraw-Hill Education, 2016. • Tille P. Bailey and Scott’s Diagnostic Microbiology. 13th edition. Elsevier Mosby, 2014.