Infections Of The Nervous System PDF

Infections of the Nervous System  the brain and its coverings can be sites of infection. some infectious agents have a relative or absolute predilection for the nervous system (e.g rabies), while others affect many other organs as well as the brain (e.g Staphylococcus aureus). Infectious agents...

Infections of the Nervous System  the brain and its coverings can be sites of infection. some infectious agents have a relative or absolute predilection for the nervous system (e.g rabies), while others affect many other organs as well as the brain (e.g Staphylococcus aureus). Infectious agents may reach the nervous system through several routes Hematogenous spread by way of the arterial blood supply is the most common means of entry. Direct implantation of microorganisms is almost invariably due to open or penetrating trauma; rare cases can be iatrogenic Cont. …. Local extension can occur with infections of the skull or spine eg. air sinuses. Peripheral nerves also may serve as paths of entry for a few pathogens—in particular, viruses such as rabies and herpes zoster. Common Central Nervous System Infections Bacterial Infections Type of Infection Clinical Syndrome Common Causative Organisms Meningitis Acute pyogenic meningitis Escherichia coli or group B streptococci (infants) Neisseria meningitidis (young adults) Streptococcus. pneumoniae or Listeria monocytogenes (older adults) Chronic meningitis Mycobacterium tuberculosis Abscess Streptococci and staphylococci Empyema Polymicrobial (staphylococci, anaerobic gram-negative) Localized infections Viral Infections Type of Infection Clinical Syndrome Common Causative Organisms Meningitis Acute aseptic meningitis Enteroviruses Measles (subacute sclerosing panencephalitis) Influenza species Lymphocytic choriomeningitis virus Encephalitis Encephalitic syndromes Arthropod-borne encephalitis Arthropod-borne encephalitis Brain stem and spinal cord syndromes Rhombencephalitis Spinal poliomyelitis Rabies Polio West Nile virus Rickettsia, Spirochetes, and Fungi Type of Infection Clinical Syndrome Common Causative Organisms Meningitic syndromes Rocky Mountain spotted fever Rickettsia rickettsii Neurosyphilis Treponema pallidum Borrelia burgdorferi Lyme disease (neuroborreliosis) Fungal meningitis Cryptococcus neoformans Candida albicans Protozoa and Metazoa Type of Infection Clinical Syndrome Common Causative Organisms Meningitic syndromes Cerebral malaria Amebic encephalitis Plasmodium falciparum Naegleria species Localized infections Toxoplasmosis Cysticercosis Toxoplasma gondii Taenia solium Acute Pyogenic Meningitis (Bacterial Meningitis) the most likely causes of bacterial meningitis vary with patient age. Age Neonates Adolescents and young adults, Older adults common organism Escherichia coli and group B streptococci. Neisseria meningitidis is Streptococcus pneumoniae and Listeria monocytogenes Cont….. across ages, patients typically show systemic signs of infection along with meningeal irritation and neurologic impairment, including headache, photophobia, irritability, clouding of consciousness, and neck stiffness. untreated pyogenic meningitis is often fatal. Cont.….. Lumbar puncture reveals an increased pressure; examination of the CSF shows  abundant neutrophils,  elevated protein  reduced glucose Morphology an exudate is evident within the leptomeninges on the surface of the brain on microscopic examination, neutrophils may fill the entire subarachnoid space or in less severe cases, may be confined to regions adjacent to leptomeningeal blood vessels. if no treatment it can lead to the formation of abscesses. A B (A) Pyogenic meningitis. A thick layer of suppurative exudate covers the brain stem and cerebellum and thickens the leptomeninges. (B) Cerebral abscesses in the frontal lobe white matter(arrows). Aseptic Meningitis (Viral Meningitis) is a clinical term for acute illness with meningeal signs and symptoms that is believed to be of viral origin. the clinical course is less fulminant and is typically self-limiting CSF examination often shows lymphocytosis, moderate protein elevation, and a normal glucose level, but bacteria cannot be cultured. there are no distinctive macroscopic findings except for brain swelling. Chronic Meningitis several pathogens, including mycobacteria, some spirochetes, and fungi, cause a chronic meningitis; infections with these organisms also may involve the brain parenchyma. Tuberculous Meningitis usually manifests with generalized signs and symptoms of headache, malaise, mental confusion, and vomiting. there is only a moderate increase in CSF cellularity, with mononuclear cells or a mixture of polymorphonuclear and mononuclear cells; the protein level is elevated, and the glucose content typically is moderately reduced or normal. Cont….. infection with Mycobacterium tuberculosis also may result in a well circumscribed intraparenchymal mass (tuberculoma), which may be associated with meningitis. meningitis leads to arachnoid fibrosis and hydrocephalus from interference with resorption of CSF. Spirochetal Infections Neurosyphilis, a tertiary stage of syphilis, occurs in about 10% of individuals with untreated Treponema pallidum infection. it often more aggressive when associated with HIV infection. There are several patterns of CNS involvement by syphilis, which may be present alone or in combination. Meningovascular neurosyphilis it a chronic meningitis, usually involving the base of the brain, often with an obliterative endarteritis rich in plasma cells and lymphocytes. Cont….. Paretic neurosyphilis stems from parenchymal involvement by spirochetes and is associated with neuronal loss and marked proliferation of microglial cells, causes an insidious progressive loss of mental and physical functions, mood alterations (including delusions of grandeur), and eventually severe dementia. Cont….. Tabes dorsalis results from damage to the sensory nerves in the dorsal roots, consequences include impaired joint position sense and ataxia; loss of pain sensation, leading to skin and joint damage (Charcot joints); other sensory disturbances, particularly characteristic “lightning pains”; and the absence of deep tendon reflexes. Parenchymal Infections the entire gamut of infectious pathogens (viruses to parasites) can infect the brain, often in characteristic patterns. in general;  viral infections are diffuse,  bacterial infections (when not associated with meningitis) are localized, while other organisms produce mixed patterns. Cont….. in immunosuppressed hosts, more widespread involvement with any agent is typical. Brain Abscesses most often caused by bacterial infections. these can arise by: direct implantation of organisms local extension from adjacent foci (mastoiditis, paranasal sinusitis) o hematogenous spread (usually from a primary site in the heart, lungs, or distal bones, or after tooth extraction). o o Cont….. predisposing conditions include:  acute bacterial endocarditis, from which septic emboli are released that may produce multiple abscesses;  cyanotic congenital heart disease, associated with a right-to-left shunt and loss of pulmonary filtration of organisms; and  chronic pulmonary infections, as in bronchiectasis, which provide a source of microbes that spread hematogenously. Cont….. Abscesses are discrete destructive lesions with central liquefactive necrosis surrounded by a rim of vascularized granulation and fibrous tissue. outside the fibrous capsule is a zone of reactive gliosis. patients almost invariably present with progressive focal deficits as well as general signs related to increased intracranial pressure. Cont….. while CSF white blood cell count and protein may be elevated, lumbar puncture has little role in the diagnosis of brain abscess since organisms are more reliably cultured by draining the abscess directly. Cont….. the increased intracranial pressure may cause fatal brain herniation, and abscess rupture can lead to ventriculitis, meningitis, and venous sinus thrombosis. Surgery and antibiotics reduce the otherwise high mortality rate, with earlier intervention leading to better outcomes. Viral Encephalitis Viral encephalitis is a parenchymal infection of the brain that is almost invariably associated with meningeal inflammation (meningoencephalitis). while different viruses show varying patterns of injury, the most characteristic histologic features are perivascular and parenchymal mononuclear cell infiltrates, microglial nodules, and neuronophagia certain viruses also form characteristic inclusion bodies. Cont….. the nervous system is particularly susceptible to certain viruses such as rabies virus and poliovirus. some viruses infect specific CNS cell types, while others preferentially involve particular brain regions (such as the medial temporal lobes, or the limbic system) that lie along the viral route of entry. Cont….. intrauterine viral infection following transplacental spread of rubella and CMV may cause destructive lesions, and Zika virus causes developmental abnormalities of the brain. in addition to direct infection of the nervous system, the CNS also can be injured by immune mechanisms after systemic viral infections. A B Characteristic findings in many forms of viral meningitis include perivascular cuffing of lymphocytes (A) and microglial nodules (B).