INFECTIONS OF NERVOUS SYSTEM

• Encephalitis


  Inflammation or infection involving the brain parenchyma
• Encephalomyelitis


  Inflammation or infection involving the brain and the spinal cord
• Meningitis


  Inflammation or infection involving the leptomeninges (pia mater and arachnoid mater)
• Meningoencephalitis


  Inflammation involving the brain and the meninges
• Myelitis


  Inflammation of the spinal cord
• The central nervous system (CNS) is impenetrable to infectious agents because it is surrounded by cerebrospinal fluid and meninges and enclosed by bones. The blood brain barrier is another structure that protects the CNS from large molecules and microorganisms. Because of these protective barriers and structures, the brain has no indigenous flora.
• Microorganisms gain access to the CNS through the bloodstream and the lymphatics and through trauma.
• Infections of the nervous system may present with non specific manifestations of fever and headache that most would consider benign. Clinical clues that will suggest infections of the nervous system include seizures, altered consciousness, or localizing signs.

  
• Acute Bacterial Meningitis


  Suppurative infection of the meninges and subarachnoid space with associated inflammation of the CNS

  
• Groups at high risk for development of bacterial meningitis

  • Children between six to twelve months of age

  
• Escherichia coli


  Most common cause of bacterial meningitis in newborns
• Group B Streptococci (Streptococcus agalactiae)


  Common cause of bacterial meningitis in newborns

  
• Listeria monocytogenes


  Common cause of bacterial meningitis in newborns, incidence increasing in the elderly and immunocompromised individuals

  
• Haemophilus influenza type b


  Most common cause of bacterial meningitis in older infants and children, incidence greatly reduced due to availability of vaccine

  
• Streptococcus pneumoniae


  Currently the most common organism that causes community acquired meningitis in children over 1 month of age and adults

  
• Neisseria meningitidis


  Also known as Meningococcus, a gram negative, coffee bean shaped (or kidney bean shaped) diplococcus that is a transient flora of the nasopharynx

  
• Mode of transmission of Neisseria meningitidis

  1. Inhalation of respiratory droplets among contacts

  2. Carriers can also transmit the infection through respiratory aerosols

  
• Neisseria meningitidis


  • Begins as throat infection, enters the bloodstream causing bacteremia and goes into the meninges causing meningitis
  • Meningococcemia (overwhelming sepsis) with or without meningitis is a life threatening infection
  • Thrombosis of small blood vessels and multi organ involvement are characteristic
  • Petechiae or purpuric skin lesions over the trunk and the lower extremities is an important presumptive sign of meningococcal infection
  • Disease may progress to massive disseminated intravascular coagulopathy with destruction of the adrenal glands called the Waterhouse Friderichsen syndrome
• Laboratory diagnosis of Neisseria meningitidis

  1. Blood and the CSF are the most useful specimens for culture

  2. Gram stain used as preliminary examination would show gram negative, coffee bean shaped (kidney bean shaped) diplococci inside polymorphonuclear cells

  
• Counter immunoelectrophoresis, agglutination, or latex particles coated with specific antibodies


  Can also be used to detect polysaccharide antigen

  
• Penicillin


  Drug of choice for treatment, but resistance is significantly increasing
• Minocycline and rifampicin


  Recommended for treatment of carriers
• Sulfonamides and rifampicin


  Recommended for prophylaxis of contacts for sulfonamide resistant strains
• Listeria monocytogenes


  Short, motile, gram positive bacilli that appear individually, in pairs or chains, cold loving but also capable of growth at 45°C and in high salt concentration

  
• Mode of transmission of Listeria monocytogenes

  Primary source of infection is ingestion of contaminated food products, but transplacental transmission is also common during pregnancy or at birth
• Listeria monocytogenes


  • Has a special affinity for growth in the CNS and the placenta
• Early onset listeriosis


  Acquired transplacentally in newborns
• Late onset listeriosis


  Acquired during or right after delivery in newborns, presents as meningitis or a combination of meningitis and encephalitis with septicemia
• Granulomatosis infantiseptica


  Severe form of early onset listeriosis which presents with granuloma and abscess formation in several organs

  
• Laboratory diagnosis of Listeria monocytogenes

  1. Diagnosis is through culture of blood, spinal fluid, or the placenta in selective media with cold enrichment

  2. Observation of tumbling end to end motility in liquid or semi solid media is also useful in initial identification

  
• Penicillin or ampicillin either singly or combined with gentamicin

  Treatment of choice for listeriosis
• Prevention of listeriosis is by avoiding eating contaminated food products and thorough washing of raw vegetables
• Granulomatous Meningitis


  Characterized by the formation of granulomas, a chronic type of meningitis commonly caused by Mycobacterium tuberculosis and Cryptococcus neoformans

  
• Tuberculous Meningitis


  Most commonly affects children younger than 6 years old, usually appears 3-6 months after initial infection and accompanies miliary tuberculosis in 50% of cases
• Tuberculous Meningitis


  • Unrelenting headache, stiff neck, fever, fatigue and night sweats are characteristics
  • Aids in diagnosis include history of contact with an adult with tuberculosis, positive tuberculin skin test, and CSF examination

  
• Quadruple anti-TB regimen


  Treatment for tuberculous meningitis
• Cryptococcus neoformans and Cryptococcus gatti

  Most common causes of fungal meningitis

  
• Cryptococcus neoformans


  • An encapsulated yeast, a common saprophyte of the soil particularly soil enriched with pigeon droppings, monomorphic (exists only as yeast) and of low virulence, opportunistic and only causes infection in immunocompromised individuals, virulence due to capsule and ability to produce melanin
• Mode of transmission of Cryptococcal meningitis

  Acquired by inhalation of the fungus from the environment, infection spreads from the lungs into the blood, affecting the CNS

  
• Cryptococcal meningitis


  • Patients may experience headaches, nausea, vomiting, loss of vision, and other focal neurologic findings of several weeks' duration, classical manifestation of meningismus is usually absent