Infectious Disease of the Brain: Meningitis & Encephalitis PDF

3 Infec(ous Disease of the Brain Recognize the most common causa(ve microorganisms of meningi(s (viral and bacterial) and encephali(s. The most common causa-ve microorganisms of meningi-s and encephali-s are: Meningi(s: 1. Bacterial Meningi(s: o Streptococcus pneumoniae: Most commo...

3 Infec(ous Disease of the Brain Recognize the most common causa(ve microorganisms of meningi(s (viral and bacterial) and encephali(s. The most common causa-ve microorganisms of meningi-s and encephali-s are: Meningi(s: 1. Bacterial Meningi(s: o Streptococcus pneumoniae: Most common cause in adults. o Neisseria meningi1dis: Common in adolescents and young adults. o Haemophilus influenzae type b (Hib): Previously common in children but has decreased due to vaccina-on. o Listeria monocytogenes: OBen affects neonates, pregnant women, and immunocompromised individuals. 2. Viral Meningi(s: o Enteroviruses (e.g., Coxsackievirus, Echovirus): Most common cause. o Herpes simplex virus (HSV-2). o Varicella-zoster virus. o Mumps virus (in regions where vaccina-on coverage is low). Encephali(s: Most cases of encephali-s are viral in origin: o Herpes simplex virus type 1 (HSV-1): Most common sporadic cause of infec-ous encephali-s. o Arboviruses: Spread through mosquitoes or -cks (e.g., West Nile virus, Japanese encephali-s virus). o Varicella-zoster virus: Can cause encephali-s in immunocompromised pa-ents. o Rabies virus: Rare but fatal if untreated. o Cytomegalovirus (CMV): Typically seen in immunocompromised individuals. Both bacterial and viral meningi-s can present with similar symptoms, including headache, fever, and neck s-ffness, but bacterial meningi-s is generally more severe and requires urgent an-bio-c treatment. Explain the pathophysiology of meningi(s and encephali(s. The pathophysiology of meningi-s and encephali-s involves dis-nct mechanisms driven by inflamma-on, infec-on, and immune responses affec-ng the brain and its protec-ve coverings. Meningi(s Pathophysiology Meningi-s is characterized by inflamma-on of the meninges, the protec-ve layers surrounding the brain and spinal cord. The key aspects of its pathophysiology are: 1. Bacterial Meningi(s: o Bacteria enter the CNS through hematogenous spread, direct extension from adjacent infec-ons (e.g., sinusi-s), or trauma-c entry.  o Neutrophils are recruited to the subarachnoid space, leading to the release of inflammatory cytokines and bacterial toxins. o Disrup-on of the blood-brain barrier allows fluid and cells to enter the CSF, resul-ng in cerebral edema and increased intracranial pressure (ICP). o The inflammatory exudate can obstruct CSF flow, causing hydrocephalus. o Damage to the blood vessels (vasculi-s) can lead to thrombosis, ischemia, or infarc-on, further contribu-ng to neuronal injury. 2. Viral Meningi(s: o Viruses typically access the CNS via the bloodstream, peripheral nerves, or infected immune cells. o Inflamma-on is generally less severe than in bacterial meningi-s, with viral invasion mainly limited to the meninges. o The immune response, including cytokine release and increased BBB permeability, combats the virus but can also cause neurological symptoms. o Viral meningi-s oBen resolves spontaneously but can be severe in neonates or immunocompromised individuals. 3. Fungal Meningi(s: o Develops slowly, oBen affec-ng immunocompromised individuals. o Fungal pathogens enter via inhala-on and hematogenous spread, leading to chronic inflamma-on in the meninges. Encephali(s Pathophysiology Encephali-s refers to inflamma-on of the brain parenchyma, most commonly due to viral infec-ons. 1. Infec(ous Encephali(s (oMen viral): o Common causes include herpes simplex virus (HSV-1), arboviruses (e.g., West Nile virus), and enteroviruses. o Viruses invade CNS cells, causing direct neuronal injury and inflamma-on. o Neuronal damage is mediated by viral replica-on, immune cell infiltra-on, and the release of pro-inflammatory cytokines. o The inflammatory response can lead to increased BBB permeability, cerebral edema, and neuronal death. o Severe cases can result in widespread neurodegenera-on, seizures, and long- term cogni-ve deficits. 2. Autoimmune and Pos(nfec(ous Encephali(s: o Autoimmune forms occur when an-bodies a\ack brain an-gens, oBen triggered by an ini-al viral infec-on. o Pos-nfec-ous encephali-s is marked by an inflammatory reac-on in the brain following systemic infec-ons, such as rubella or measles. In summary, meningi-s involves inflamma-on of the meninges primarily due to infec-ous agents, leading to cerebral edema, increased ICP, and poten-al hydrocephalus. In contrast, encephali-s is characterized by direct viral invasion or immune-mediated inflamma-on of the brain parenchyma, leading to widespread neuronal damage and func-onal impairments. Describe the clinical manifestations of meningitis and encephalitis. Clinical Manifesta(ons of Meningi(s: Meningi-s is characterized by the inflamma-on of the meninges and can be caused by bacterial, viral, or fungal infec-ons. The symptoms can be categorized into three primary groups: 1. Infec(ous Signs: o Fever o Tachycardia o Chills 2. Meningeal Signs: o Severe throbbing headache o Severe photophobia (sensi-vity to light) o Nuchal rigidity (neck s-ffness) o Posi-ve Kernig and Brudzinski signs 3. Neurological Signs (due to increased intracranial pressure): o Decrease in consciousness o Cranial nerve palsies o Focal neurological deficits (e.g., hemiparesis/hemiplegia, ataxia) o Seizures o Projec-le vomi-ng o Papilledema (swelling of the op-c disc) o In severe cases, progression to delirium, unconsciousness, or death Special Presenta(on: Meningococcal meningi-s may present with a petechial or purpuric rash covering the skin and mucous membranes. Clinical Manifesta(ons of Encephali(s: Encephali-s is an acute inflamma-on of the brain typically of viral origin, though it may also result from autoimmune or pos-nfec-ous causes. 1. General Symptoms: o Fever o Headache o Altered level of consciousness ranging from confusion to coma o Seizures o Focal neurological deficits such as weakness or aphasia (depending on the area of the brain affected) 2. Specific Viral Features: o Herpes simplex virus type 1 is a common cause of sporadic encephali-s and may lead to significant damage to the temporal lobe, causing memory issues and behavioral disturbances. o Other viral causes (e.g., arboviruses, varicella, and rubella) may present with systemic symptoms like a rash or signs of generalized infec-on. 3. Progression: Severe cases may result in permanent neurological damage, such as cogni-ve impairment or motor deficits.