NEET MDS Lessons
General Pathology
Staphylococcal Infection
Staphylococci, including pathogenic strains, are normal inhabitants of the nose and skin of most healthy people
Virulence factors include coagulase (which clots blood), hemolysin, and protein A (which ties up Fc portions of antibodies). Although we have antibodies against staphylococci, they are of limited usefulness.
Staphylococci (and certain other microbes) also produce catalase, which breaks down H2O2, rendering phagocytes relatively helpless against them.
The coagulase-positive staphylococcus (Staphylococcus pyogenes var. aureus) is a potent pathogen. It tends to produce localized infection
It is the chief cause of bacterial skin abscesses. Infection spreads from a single infected hair (folliculitis) or splinter to involve the surrounding skin and subcutaneous tissues
Furuncles are single pimples
carbuncles are pimple clusters linked by tracks of tissue necrosis which involve the fascia.
Impetigo is a pediatric infection limited to the stratum corneum of the skin -- look for honey-colored crusts
Staphylococcal infections of the nail-bed (paronychia) and palmar fingertips (felons) are especially painful and destructive
These staph are common causes of wound infections (including surgical wounds) and of a severe, necrotizing pneumonia. Both are serious infections in the hospitalized patient.
Staph is the most common cause of synthetic vascular graft infections. Certain sticky strains grow as a biofilm on the grafts
Staph aureus is pathogenic, β-hemolytic, and makes coagulase.
Staph epidermidis are non-pathogenic strains that don’t make coagulase. Often Antibiotics resistant, and can become opportunistic infections in hospitals.
Staph aureus is normal flora in the nose and on skin, but can also colonize moist areas such as perineum. Causes the minor infections after cuts. Major infections occur with lacerations or immune compromise, where large number of cocci are introduced.
While Staph aureus can invade the gut directly (invasive staphylococcal enterocolitis), it is much more common to encounter food poisoning due to strains which have produced enterotoxin B, a pre-formed toxin in un-refrigerated meat or milk products
Staph epidermidis (Coagulase-negative staphylococci)
Universal normal flora but few virulence factors. Often antibiotic resistant.
Major cause of foreign body infections such as prosthetic valve endocarditis and IV line sepsis.
Staph saprophyticus
Common cause of UTI in women.
Pathogenicity
Dominant features of S. aureus infections are pus, necrosis, scarring. The infections are patchy. Serious disease is rare because we are generally immune. However, foreign bodies or necrotic tissue can start an infection. Staph infections include wound infections, foreign body sepsis, pneumonia, meningitis.
Occassionally, S. aureus can persist within cells.
Major disease presentations include:
--Endocarditis
--Abscesses (due to coagulase activity)
--Toxic Shock
--Wound infections
--Nosocomial pneumonia
Prevention of Staph aureus infections
S. aureus only lives on people, so touching is the main mode of transmission. Infected patients should be isolated, but containment is easy with intense hand washing.
Thyroid goitres
A goitre is any enlargement of part or whole of the thyroid gland. There are two types:
1. Toxic goitre, i.e. goitre associated with thyrotoxicosis.
2. Non-toxic goitre, i.e. goitre associated with normal or reduced levels of thyroid hormones.
Toxic goitre
Graves disease
This is the most common cause of toxic goitre
Toxic multinodular goitre
This results from the development of hyperthyroidism in a multinodular goitre
Non-toxic goitres
Diffuse non-toxic goitre (simple goitre)
This diffuse enlargement of the thyroid gland is classified into:
Endemic goitre—due to iodine deficiency. Endemic goiter occurs in geographic areas (typically mountainous)) where the soil, water, and food supply contain little iodine. The term endemic is used when goiters are present in more than 10% of the population in a given region. With increasing availability of dietary iodine supplementation, the frequency and severity of endemic goiter have declined significantly. Sporadic goiter is less common than endemic goiter. The condition is more common in females than in males, with a peak incidence in puberty or young adult life, when there is an
increased physiologic demand for T4.
Sporadic goitre—caused by goitrogenic agents (substances that induce goitre formation) or familial in origin. Examples of goitrogenic agents include certain cabbage species, because of their thiourea content, and specific drugs or chemicals, such as iodide, paraminosalicylic acid and drugs used in the treatment of thyrotoxicosis. Familial cases show inherited autosomal recessive traits, which interfere with hormone synthesis via various enzyme pathways (these are dyshormonogenic goitres).
Hereditary enzymatic defects interfering with thyroid hormone synthesis (dyshormonogenetic goiter).
Physiological goitre—enlargement of the thyroid gland in females during puberty or pregnancy; the reason is unclear.
Multinodular goitre
This is the most common cause of thyroid enlargement and is seen particularly in the elderly (nearly all simple goitres eventually become multinodular). The exact aetiology is uncertain but it may represent an uneven responsiveness of various parts of the thyroid to fluctuating TSH levels over a period of many years.
Morphological features are:
• Irregular hyperplastic enlargement of the entire thyroid gland due to the development of wellcircumscribed nodules of varying size.
• Larger nodules filled with brown, gelatinous colloid; consequently, it is often termed multinodular colloid goitres.
Clinical features
- A large neck mass, goiters may also cause airway obstruction, dysphagia, and compression of large vessels in the neck and upper thorax.
- A hyperfunctioning ("toxic") nodule may develop within a long-standing goiter, resulting in hyperthyroidism. This condition is not accompanied by the infiltrative ophthalmopathy and dermopathy.
- Less commonly, there may be hypothyroidism.
Paroxysmal nocturnal haemoglobinuria (PNH).
Feature:
- Acquired RBC rnembrane defect rendering it susceptible to complement lysis.
- Features of intravascular haemolysis.
- Blood picture of haemolysis anemais with pancytopenia.
- Ham’s acid serum test (lysis at 37COin acid pH) + ve
Osteopetrosis (Albers-Schönberg disease or marble bone disease)
is a group of rare genetic disorders characterized by reduced osteoclast-mediated bone resorption and therefore defective bone remodelling. The bones are solid and heavy with no medullary canal, long ends are bulbous, small neural foramina compress nerves. The affected bone is grossly dense but fractures occur readily like a piece of chalk.
Patients frequently have cranial nerve compressions by the surrouding bone, and recurrent infections. The latter is attributable to diminished hematopoiesis resulting from reduced marrow space with impressive hepatosplenomegaly due to extramedullary hematopoiesis
a. Caused by abnormal osteoclasts. This results in defective bone remodeling (i.e., abnormally low bone resorption) and increased bone density, which may invade into bone marrow space.
b. Causes severe defects in infants, including:
(1) Anemia and infections—caused by decreased bone marrow.
(2) Blindness, deafness, paralysis of facial muscles—caused by the narrowing of cranial nerve foramina.
(3) Is life-threatening.
(4) Oral findings include delayed eruption of teeth.
c. Disease is less severe in adults
Fulminant hepatitis
Fulminant hepatitis leads to submassive and massive hepatic necrosis.
a. Etiology. HAV, HBV, HCV, delta virus (HDV) superinfection, HEV, chloroform, carbon tetrachloride, isoniazid, halothane, and other drugs (acetaminophen overdose) all may cause fulminant hepatitis.
b. Clinical features include progressive hepatic dysfunction with a mortality of 25%-90%.
c. Pathology
(1) Grossly, one sees progressive shrinkage of the liver as the parenchyma is destroyed.
Microbiological examination
This is a method by which body fluids, excised tissue, etc. are examined by microscopical, cultural and serological techniques to identify micro-organisms Microbiological examination responsible for many diseases.
Alzheimer’s disease
a. The most common cause of dementia in older people.
b. Characterized by degeneration of neurons in the cerebral cortex.
c. Histologic findings include amyloid plaques and neurofibrillary tangles.
d. Clinically, the disease takes years to develop and results in the loss of cognition, memory, and the ability to ommunicate. Motor problems, contractures, and paralysis are some of the symptoms at the terminal stage.