NEET MDS Lessons
General Pathology
HAEMORRHAGIC DISORDERS
Normal homeostasis depends on
-Capillary integrity and tissue support.
- Platelets; number and function
(a) For integrity of capillary endothelium and platelet plug by adhesion and aggregation
(b) Vasoactive substances for vasoconstriction
(c) Platelet factor for coagulation.
(d) clot retraction.
- Fibrinolytic system(mainly Plasmin) : which keeps the coagulation system in check.
Coagulation disorders
These may be factors :
Deficiency .of factors
- Genetic.
- Vitamin K deficiency.
- Liver disease.
- Secondary to disseminated intravascular coagulation.or defibrinatian
Overactive fibrinolytic system.
Inhibitors of the factors (immune, acquired).
Anticoagulant therapy as in myocardial infarction.
Haemophilia. Genetic disease transmitted as X linked recessive trait. Common in Europe. Defect in fcatorVII Haemophilia A .or in fact .or IX-Haemaphilia B (rarer).
Features:
- May manifest in infancy or later.
- Severity depends on degree of deficiency.
- Persistant wound bleeding.
- Easy Bruising with Hematoma formation
Nose bleed , arthrosis, abdominal pain with fever and leukocytosis
Prognosis is good with prevention of trauma and-transfusion of Fresh blood or fTesh plasma except for danger of developing immune inhibitors.
Von Willebrand's disease. Capillary fragility and decreased factor VIII (due to deficient stimulatory factor). It is transmitted in an autosomal dominant manner both. Sexes affected equally
Vitamin K Deficiency. Vitamin K is needed for synthesis of factor II,VII,IX and X.
Deficiency maybe due to:
Obstructive jaundice.
Steatorrhoea.
Gut sterilisation by antibiotics.
Liver disease results in :
Deficient synthesis of factor I II, V, Vll, IX and X Incseased fibrinolysis (as liver is the site of detoxification of activators ).
Defibrination syndrome. occurs when factors are depleted due to disseminated .intravascular coagulation (DIC). It is initiated by endothelial damage or tissue factor entering the circulation.
Causes
Obstetric accidents, especially amniotic fluid embolism. Septicaemia. .
Hypersensitivity reactions.
Disseminated malignancy.
Snake bite.
Vascular defects : (Non thrombocytopenic purpura).
Acquired :
Simple purpura a seen in women. It is probably endocrinal
Senile parpura in old people due to reduced tissue support to vessels
Allergic or toxic damage to endothelium due to Infections like Typhoid Septicemia
Col!agen diseases.
Scurvy
Uraemia damage to endothelium (platelet defects).
Drugs like aspirin. tranquillisers, Streptomvcin pencillin etc.
Henoc schonlien purpura Widespeard vasculitis due to hypersensitivity to bacteria or foodstuff
It manifests as :
Pulrpurric rashes.
Arthralgia.
Abdominal pain.
Nephritis and haematuria.
Hereditary :
(a) Haemhoragic telangieclasia. Spider like tortous vessels which bleed easily. There are disseminated lesions in skin, mucosa and viscera.
(b) Hereditary capillary fragilily similar to the vascular component of von Willbrand’s disease
.(c) Ehler Danlos Syndrome which is a connective tissue defect with skin, vascular and joint manifestations.
Platelet defects
These may be :
(I) Qualitative thromboasthenia and thrombocytopathy.
(2) Thrombocytopenia :Reduction in number.
(a) Primary or idiopathic thrombocytopenic purpura.
(b) Secondary to :
(i) Drugs especially sedormid
(ii) Leukaemias
(iii) Aplastic-anaemia.
Idiopathic thrombocytopenic purpura (ITP). Commoner in young females.
Manifests as :
Acute self limiting type.
Chronic recurring type.
Features:
(i) Spontaneous bleeding and easy bruisability
(ii)Skin (petechiae), mucus membrane (epistaxis) lesions and sometimes visceral lesions involving any organ.
Thrombocytopenia with abnormal forms of platelets.
Marrow shows increased megakaryocytes with immature forms, vacuolation, and lack of platelet budding.
Pathogenesis:
hypersensitivity to infective agent in acute type.
Plasma thrombocytopenic factor ( Antibody in nature) in chronic type
Salivary gland pathology
Inflammation
a. Sialolithiasis produces a secondary inflammatory reaction to obstruction and the resultant enlargement of ducts by stones. It may be complicated by actual infection with mouth flora.
b. Sialadenitis is a primary inflammatory reaction, but it is not always infectious. It may be part of an autoimmune disease (e.g., Sjogren's syndrome), or the result of bacterial or virals (e.g., mumps) infection.
Sjögren’s syndrome
a. An autoimmune disease of the salivary and lacrimal glands.
b. Autonuclear antibodies (ANAs) against salivary ducts may be seen.
c. Triad of symptoms include:
(1) Xerostomia—from decreased saliva production.
(2) Keratoconjunctivitis sicca (dry eyes)—from decreased tear production.
(3) Rheumatoid arthritis.
(4) Enlargement of the salivary or lacrimal glands, known as Mikulicz syndrome, may also be observed.
d. Histologically, a dense infiltration of the gland by lymphocytes is observed.
Tumors
The parotid gland accounts for more than three-quarters of these tumors, most of which are benign. Of the remainder, more occur in the submandibular gland than in the sublingual, and most of these are malignant. Many are surgically, cured, but local recurrence is common.
a. Pleomorphic adenoma is generally benign and accounts for approximately three-quarters of all salivary gland tumors. If is composed of multiple epithelial and mesenchymal cell types. Complications may arise due to involvement of cranial nerve VII.
(a) The most common salivary gland tumor.
(b) Is benign.
(c) Prognosis is good after proper surgical excision.
b. Warthin's tumor (adenolymphoma) is also benign, occuring almost exclusively in the parotid gland. It is grossly cystic.
Microscopic examination reveals cell types suggestive of branchial cleft origin embedded in a lymphoid matrix.
c. Mucoepidermoid tumors also occur primarily in the parotid and have a high rate of malignant transformation.The malignant component is usually squamous cell. Prognosis of tumor depends on grade and stage of disease.
d. Cylindroma (adenoid cysticc. Mucoepidermoid tumors carcinoma) is more common in the minor salivary glands found in the oral mucosa, and metastases are more common than in other tumors of the salivary glands. Facial nerve complications are frequent.
(1) Grossly, the tumor forms multiple lobules surrounded by a capsule.
(2) Microscopically, small cells form glands containin mucoid material
Group A Streptococcus
- scarlet fever usually begins as a Streptococcal pharyngitis/tonsillitis and then develops an erythematous rash beginning on the trunk and limbs with eventual desquamation.
- rash is due to elaboration of erythrogenic toxin by the organism
- face is usually spared, but, if involved there is a characteristic circumoral pallor and the tongue becomes bright red, thus the term "strawberry tongue".
- post-streptococcal immune complex glomerulonephritis is a possible sequela of scarlet fever.
- Dick test is a skin test that evaluates immunity against scarlet fever; no response indicates immunity (anti-toxin antibodies present); erythema indicates no immunity.
- impetigo due to Streptococcus pyogenes is characterized by honey colored, crusted lesions, while those with a predominantly bullous pattern are primarily due to Staphylococcus aureus.
- cellulitis with lymphangitis ("red streaks") is characteristic of Streptococcus pyogenes.
- hyaluronidase is a spreading factor that favors the spread of infection throughout the subcutaneous tissue unlike Staphylococcus aureus which generates coagulase to keep the pus confined.
- erysipelas refers to a raised, erythematous ("brawny edema"), hot cellulitis, usually on the face that commonly produces septicemia, if left untreated.
Enterococci
Most common are E. fecalis and E. fecium. Cause inflammation at site of colonization.
Serious resistance to antibiotics. E. fecium is now a vancomycin resistant enterococcus (VRE)
PRIMARY LYMPHEDEMA
can occur as:
1- A congenital defect, resulting from lymphatic agenesis or hypoplasia.
2- Secondary or obstructive lymphedema
- blockage of a previously normal lymphatic; e.g. Malignant tumors
- Surgical procedures that remove lymph nodes
- Postirradiation
- Fibrosis
- Filariasis
- Postinflammatory thrombosis and scarring
Roseola
- alias exanthem subitum; caused by Herpes virus type 6.
- children 6 months to 2 years old; spring and fall; incubation 10-15 days.
- sudden onset of a high fever with absence of physical findings; febrile convulsions are particularly common.
- fever falls by crisis on the 3rd or 4th day → 48 hours after temperature returns to normal macular or maculopapular rash starting on the trunk and spreading centrifugally.
VIRAL DISEASES
RABIES (Hydrophobia)
An acute infectious disease of mammals, especially carnivores, characterized by CNS pathology leading to paralysis and death.
Etiology and Epidemiology
Rabies is caused by a neurotropic virus often present in the saliva of rabid animals
Pathology
The virus travels from the site of entry via peripheral nerves to the spinal cord and the brain, where it multiplies; it continues through efferent nerves to the salivary glands and into the saliva.
microscopic examination shows perivascular collections of lymphocytes but little destruction of nerve cells. Intracytoplasmic inclusion bodies (Negri bodies), usually in the cornu Ammonis, are pathognomonic of rabies, but these bodies are not always found.
Sign/Symptoms
In humans, the incubation period varies from 10 days to > 1 yr and averages 30 to 50 days.
Rabies commonly begins with a short period of depression, restlessness, malaise, and fever. Restlessness increases to uncontrollable excitement, with excessive salivation and excruciatingly painful spasms of the laryngeal and pharyngeal muscles. The spasms, which result from reflex irritability of the deglutition and respiration centers, are easily precipitated Hysteria due to fright
Prognosis and Treatment
Death from asphyxia, exhaustion, or general paralysis usually occurs within 3 to 10 days after onset of symptoms