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General Pathology - NEETMDS- courses
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General Pathology

N. meningiditis

Major cause of fulminant bacteremia and meningitis.  Has a unique polysaccharide capsule.  It is spread person to person by the respiratory route.  Frequently carried in nasopharynx, and carriage rates increased by close quarters.  Special risk in closed populations (college dorms) and in people lacking complement.  Sub-saharan Africa has a “meningitis belt.”

Pathogenesis is caused by adherence factors that attach to non-ciliated nasopharyngeal epithelium. These factors include pili which promote the intial epithelial (and erythrocyte) attachment, and Opa/Opc surface binding proteins.

Adherence stimulates engulfment of bacteria by epithelial cells.  Transported to basolateral surface.

The polysaccharide capsule is a major virulence factor that prevents phagocytosis and lysis. 

A lipo-oligosaccharide endotoxin also contributes to sepsis.

Neutrophilia
Causes
    
-Pyogenic infections.
-Haemorrhage and trauma.
-Malignancies.
-Infarction.
-Myelo proliferative disorders.

AMYLOIDOSIS

Definition. Extra cellular  deposition of an eosinophilic hyaline homogenous material in Various organs, occurring in a variety of clinical  states.

Staining reactions

Iodine :- Brown, turning blue on addition of H2SO4 (gross and microscopic Stain).
P.A.S. – Positive  (Magenta pink).
Congo Red -Orange red which on polarisation gives green birefringence.
Von Geison's –Khaki colour.
Thioflavin T -Yellow fluorescence.

Amyloid is called typical if it given the above staining  reactions Other wise it is termed atypical or para-amyloid.

Classification 

1.    Systemic  amyloidosis associated with underlying disease (secondary),

(A) Chronic infections like 

- Tuberculosis.
- Bronchiectasis.
- Lung abscess.
- Osteomyelitis.
- Syphilis.

(B) Chronic inflammations of varied etiology:

- Rheumatoid arthritis.
- Ulcerative colitis.
- Regional enteritis.
- Lupus erythematosus.

(C) Neoplastic proliferations:

- Of immune system – Multiple myeloma, Hodgkin’s disease.
- Cancers like Renal cell carcinoma etc.


II Systemic primary amyloidosis  with no underlying cause.

III Heredofamilial types.

- Amyloidosis with mediterranean fever.
- Amyloid polyneuropathy.
- Amyloid nephrophathy
- Familial cardiac amyloidosis
- Familial cutaneous amyloid.
- Lattice corneal dystrophy

IV. Localised amyloidosis:

- Senile - in heart, brain, seminal vesicles.
- Amyloidoma of tongue, bronchial tree, skin.
- In islets of Langerhans in Diabetes mellitus.
- In medullary thyroid carcinoma.

Deposition sites
In relation to reticulin  and collagen fibres and to basement, membranes especially
subendothelial. 

Organs involved commonly are : 

Secondary amyloidosis

- Liver.
- Spleen.
- Kidney
- Lymph nodes.
- Adrenals.

Primary amyloidosis

- Heart
- Tongue and gingiva.
- Gastro intestinal tract.
- Lung.
- Wall of small vessels.

Nature and pathogenesis of amyloid
It is primarily made up of protein arranged in two patterns

- There are filaments twisted together to from the fibrils. These chemically resemble light chains of immunoglobulins
- Rods composed of stacked rings. These are made up of alpha globulin components of plasma proteins (P-components)

- In addition to these, extracts of crude amyloid contain  mucopolysacharides complement and gamma globulins.

- Origin of amyloid :- current concept is that it is a direct product of cells of the immune sustem with some abnormality in their immune response

The abnormality may be due to :
- A genetic enzyme defect.
- Prolonged antigenic challenge.
- Neoplastic transformation
- Supression of normal. Response as in induced tolerance.

 IMMUNO PATHOLOGY
Abnormalities of immune reactions are of 3 main groups
- Hypersensitivity,
- Immuno deficiency,
- Auto immunity.
Hypersensitivity (ALLERGY)
This is an exaggerated or altered immune response resulting in adverse effects

They are classified into 4 main types.

I. Type I-(reaginic, anaphylactic). This is mediated by cytophylic Ig E antibodies, which get bound to mast cells. On re-exposure, the Ag-Ab reaction occurs on the mast cell surface releasing histamine.

Clinical  situations

I. Systemic anaphylaxis, presenting with bronchospasm oedema hypertension, and even death.
2. Local (atopic) allergy.
- Allergic rhinitis (hay fever)
- Asthma
- Urticaria.
- Food allergies.

2. Type II. (cytotoxic). Antibody combines with antigen present on-cell surface. The antigen may be naturally present on the surface or an extrinsic substance (e.g.drug) attached to cell surface.

The cell is then destroyed by complement mediated lysis (C89) or phagocytosis of the antibody coated cell. 

Clinical situations

- Haemolytic anemia.
- Transfusion reaction
- Auto immune haemolytic anemia.
- Haemolysis due to some drugs like Alpha methyl dopa

2. Drug induced thrombocytopenia (especially sedormid).
3 Agranulocytosis due to sensitivity to some drugs.
4 Goodpasture’s syndrome-glomermerulonephritis due to anti basement membrane antibodies.

3. Type III. (Immune complex disease). Circulating immune complexes especially small soluble complexes tend to deposit in tissues especially kidney, joints, heart and arteries.

These then cause clumping of platelets with subsequent release of histamine. and serotonin resulting in increased permeability. Also, complement activation occurs which being chemotactic results in aggregation of polymorphs and necrotising vasculitis due to release of lysosmal enzymes

Clinical situations

- Serum sickness.
- Immune complex glomerulonephritis.
- Systemic lupus erythematosus.
- Allergic alveolitis.
- Immune based vasculitis like
    o    Drug induced vasculitis.
    o    Henoch – Schonlein purpura

4. Type IV. (Cell mediated). The sensitized lymphocytes may cause damage by cytotoxicity or by lymphokines and secondarily involving macrophages in the reaction.

Clinical situations

I. Caseation necrosis in tuberculosis.
2. Contact dermatitis to
    - Metals.
    - Rubber.
    - Drugs (topical).
    - Dinitrochlorbenzene (DNCB).
    
5. Type V. (stimulatory) This is classed by some workers separately and by other with cytotoxic type (Type II) with a stimulatory instead of toxic effect

Clinical Situations :
LATS (long acting thyroid stimulator) results in thyrotoxicosis (Grave’s disease)
 

HERPES SIMPLEX

An infection with herpes simplex virus characterized by one or many clusters of small vesicles filled with clear fluid on slightly raised inflammatory bases.

The two types of herpes simplex virus (HSV) are HSV-1 and HSV-2. HSV-1 commonly causes herpes labialis, herpetic stomatitis, and keratitis; HSV-2 usually causes genital herpes, is transmitted primarily by direct (usually sexual) contact with lesions, and results in skin lesions

Primary infection of HSV-1 typically causes a gingivostomatitis, which is most common in infants and young children. Symptoms include irritability, anorexia, fever, gingival inflammation, and painful ulcers of the mouth.

Primary infection of HSV-2 typically occurs on the vulva and vagina or penis in young adults

Herpetic whitlow, a swollen, painful, and erythematous lesion of the distal phalanx, results from inoculation of HSV through a cutaneous break or abrasion and is most common in health care workers.

Herpes simplex is subdivided into type 1 and 2, the former usually developing lesions around the lips and mouth and the latter producing vesicular lesions in the genital region 
 - contracted by physical contact; incubation 2-10 days.
 - primary HSV I usually is accompanied by systemic signs of fever and Lymphadenopathy, while recurrent herpes is not associate with systemic signs.
 - dentists often become infected by contact with patient saliva and often develop extremely painful infections on the fingers (herpetic whitlow).
 - Herpes viruses remain dormant in sensory ganglia and are reactivated by stress, sunlight, menses, etc. 

 - Herpes gingivostomatitis is MC primary HSV 1 infectionÆpainful, vesicular eruptions that may extend for the tongue to the retropharynx.
 - Herpes keratoconjunctivitis (HSV 1)
 - Kaposi's varicelliform eruption refers to an HSV 1 infection superimposed on a previous dermatitis, usually in an immunodeficient person.
 - laboratory: culture; ELISA test on vesicle fluid; intranuclear inclusions within multinucleated squamous cells in scrapings (Tzanck preps) of vesicular lesions. 

Clinical genetics (cytogenetics),

This is a method in which inherited chromosomal abnormalities in the germ cells or acquired chromosomal abnormalities in somatic cells are investigated using the techniques of molecular biology.

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