NEET MDS Lessons
General Pathology
Hepatitis D virus—can only infect cells previously infected with hepatitis B.
Delta hepatitis (HDV) is associated with a 35-nm RNA virus composed of a delta antigen-bearing core surrounded by HBV's Ag coat;
HDV requires HBV for replication.
Delta hepatitis can cause quiescent HBV states to suddenly worsened . Its transmission is the same as that of HBV.
Hepatitis E virus—a high mortality rate in infected pregnant women.
Hepatitis E (HEV) is caused by a single-stranded RNA virus. The disease is typically self-limited and does not evolve into chronic hepatitis; it may, however, be cholestatic.
Pregnant women may develop fulminant disease.
Transmission is by the fecal oral route.
HEV occurs mainly in India, Nepal, Pakistan, and Southeast Asia.
Sickle Cell Disease
Sickle cell anemia is a autosomal recessive genetic disorder. It affects the BETA GLOBIN gene on the CHROMOSOME 16. In sickle cell anemia, the hemoglobin abnormality consists of a point mutation in the beta chain gene for hemoglobin; the resulting abnormal gene product is denoted HbS. If you are heterozygous for the HbS gene you will have what is called sickle trait, which is asymptomatic .
If you are homozygous for the HbS gene you will get sickle cell disease, which is symptomatic in most patients.
The problem with HbS is that as it releases oxygen, it polymerizes and aggregates with other HbS molecules, making the red cell stiff and distorted. These distorted, sickle-shaped red cells are fragile so the patient can end up with a hemolytic anemia.
This can occur as pure disease (homozygous) or trait (heterozygous) or with other haemoglobinopathies. It is common. in Negroes. It is due to Hb-s which is much less soluble than Hb-A hence deoxygenation insoluble form sickling of RBC.
This causes:
• Removal by RE system.
• Blockage of microvessels causing ischaemia.
EXOCRINE PANCREAS
Congenital anomalies
1. Ectopic pancreatic tissue most commonly occurs in the stomach, duodenum, jejunum, Meckel's diverticulum, and ileum. It may be either asymptomatic or cause obstruction, bleeding, intussusception.
2.Annular pancreas is a ring of pancreatic tissue that encircle the duodenum and may cause duodenal obstruction.
Cystic fibrosis
Cystic fibrosis is a systemic disorder of exocrine gland secretion presenting during infancy or childhood.
Incidence is 1:2500 in Caucasians; it is less common in Black and extremely rare in Asians.
Pathogenesis. Cystic fibrosis shows autosomal recessive transmission; heterozygotes are unaffected. It results in a defective chloride channel, which leads to secretion of very thick mucus.
Characteristics
- Tissues other than exocrine glands are normal, and glands are structurally normal until damaged by cystic fibrosis.
- The only characteristic biochemical abnormalities are an elevation of sodium and chloride levels in sweat, and a decrease in water and bicarbonate secretion from pancreatic cells, resulting in a viscous secretion.
Clinical features
- Fifteen percent of cases present with meconium ileus.
- Most cases present during the first year with steatorrhea (with resultant deficiencies of vitamins A, D, E, and K), abdominal distention, and failure to thrive.
Complications are also related to pulmonary infections'and obstructive pulmonary disease as a result of viscous bronchial secretions.
Pathology
- There is mucus plugging of the pancreatic ducts with cystic dilatation, fibrous proliferation, and atrophy. Similar pathology develops in salivary glands.
- Lungs. Mucus impaction leads to bronchiolar dilatation an secondary infection.
- The gastrointestinal tract shows obstruction caused mucus impaction in the intestines with areas of biliary cirrhosis, resulting from intrahepatic bile duct obstruction
Diagnosis depends on demonstrating a "sweat test" abnomality associated with at least one clinical feature In sweat test, high levels of chloride are demonstrated.
Prognosis. Mean survival is age 20; mortality is most often due to pulmonary infections.
Degenerative changes
1. Iron pigmentation (e.g., from hemochromatosis) may be deposited within acinar and islet cells and may cause insulin deficiency.
2. Atrophy
a. Ischemic atrophy is due to atherosclerosis of pancreatic arteries and is usually asymptomatic.
b. Obstruction of pancreatic ducts affects only the exocrine pancreas, which becomes small, fibrous, and nodular.
Acute hemorrhagic pancreatitis
presents as a diffuse necrosis of the pancreas caused by the release of activated pancreatic
enzymes. Associated findings include fat necrosis and hemorrhage into the pancreas.
Incidence. This disorder is most often associated with alcoholism and biliary tract disease.
It affects middle-aged individuals and often occurs after a large meal or excessive alcohol ingestion; approximately 50% of patients have gallstones.
Pathogenesis. There are four theories.
- Obstruction of the pancreatic duct causes an elevated intraductal pressure, which results in leakage of enzymes from small ducts.
- obstruction may be caused by a gallstone at the ampulla of Vater; chronic alcohol ingestion may cause duct obstruction by edema.
- Hypercalcemia may cause activation of trypsinogen; its mechanism is unclear. Pancreatitis occurs in 20% of patients with hyperparathyroidism.
- Direct damage to acinar cells may occur by trauma, ischemia, viruses, and drugs.
- Hyperlipidemia may occur as a result of exogenous estrogen intake and alcohol ingestion.
Clinical features are typically the sudden onset of acute, continuous, and intense abdominal pain, often radiating to the back and accompanied by nausea, vomiting, and fever. This syndrome frequently results in shock.
Laboratory values reveal elevated amylase (lipase elevated after 3-4 days) and leukocytosis. Hypocalcemia is a poor prognostic sign.
Chronic pancreatitis
It refers to remitting and relapsing episodes of mild pancreatitis, causing progressive pancreatic damage.
Incidence is similar to acute pancreatitis. It is also seen in patients with ductal anomalies. Almost half the cases occur without known risk factors.
Pathogenesis is unclear; possibly, there is excess protein secretion by the pancreas, causing ductal obstruction.
Clinical features include flareups precipitated by alcohol and overeating, and drugs. Attacks are characterized by upper abdominal pain, tenderness, fever, and jaundice.
Laboratory values reveal elevated amylase and alkaline phosphatase, X-rays reveal calcifications in the pancreas. Chronic pancreatitis may result in pseudocyst formation, diabetes, and steatorrhea.
Carcinoma of the pancreas
Incidence:
Carcinoma of the pancreas accounts for approximately 5% of all cancer deaths. Increased risk is associated with smoking. high-fat diet, and chemical exposure. There is a higher incidence in the elderly, Blacks, males, and diabetics.
Clinical features
- The disease is usually asymptomatic until late in its course.
- Manifestations include weight loss, abdominal pain frequently radiating to the back, weakness, malaise, anorexia, depression, and ascites.
- There is jaundice in half of the patients who have carcinoma of the head of the pancreas.
- Courvoisier's law holds that painless jaundice with a palpable gallbladder is suggestive of pancreatic cancer.
Pathology
Carcinomas arise in ductal epithelium. Most are adenocarcinomas.
- Carcinoma of the head of the pancreas accounts for 60% of all pancreatic cancers.
- Carcinoma of the body (20%) and tail (5%) produce large indurated masses that spread widely to the liver and lymph nodes.
- In 15% of patients, carcinoma involves the pancreas diffusely.
Complications
include Trousseau's syndrome, a migratory thrombophlebitis that occurs in 10% of patients.
Prognosis is very poor. if resectable, the 5-year survival rate less than 5%. The usual course is rapid decline; on average death occurs 6 months after the onset of symptoms.
Chronic lymphocytic leukaemia
Commoner in middle age. It starts insidiously and often runs a long chronic course
Features:
- Lymphnode enlargement.
- Anaemia (with haemolytic element).
- Moderate splenomegaly.
- Haemorrhagic tendency in late stages.
- Infection.
Blood picture:
- Anaemia with features of haemolytic anaemia
- Total leucocytic count of 50-100,OOO/cu.mm.
- Upto 90-95% cells are lymphocytes and prolymphocytes.
- Thrombocytopenia may be seen.
Bone marrow. Lymphocytic series cells-are seen. Cells of other series are reduced,
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
Cardiac tamponade
A. Caused by accumulation of fluid in the pericardium. This severe condition can quickly impair ventricular filling and rapidly lead to decreased cardiac output and death.
1. Signs and symptoms include:
a. Hypotension.
b. Jugular venous distention.
c. Distant heart sounds.
Cardiac arrhythmia
Cardiac arrhythmia is a group of conditions in which muscle contraction of the heart is irregular for any reason.
Tachycardia :A rhythm of the heart at a rate of more than 100 beats/minute , palpitation present
Causes : stress, caffeine, alcohol, hyperthyroidism or drugs
Bradycardia : slow rhythm of the heart at a rate less than 60 beats/min
Atrial Arrhythmias
- Atrial fibrillation
Atrial Dysrhythmias
- Premature atrial contraction
- Atrial flutter
- Supraventricular tachycardia
- Sick sinus syndrome
Ventricular Arrhythmias
- Ventricular fibrillation
Ventricular Dysrhythmias
- Premature ventricular contraction
- Pulseless electrical activity
- Ventricular tachycardia
- Asystole
Heart Blocks
- First degree heart block
- Second degree heart block
o Type 1 Second degree heart block a.k.a. Mobitz I or Wenckebach
o Type 2 Second degree heart block a.k.a. Mobitz II
- Third degree heart block a.k.a. complete heart block
Atrial fibrillation
Atrial fibrillation is a cardiac arrhythmia (an abnormality of heart rate or rhythm) originating in the atria.
AF is the most common cardiac arrhythmia
Signs and symptoms
Rapid and irregular heart rates
palpitations, exercise intolerance, and occasionally produce angina and congestive symptoms of shortness of breath or edema
Paroxysmal atrial fibrillation is the episodic occurence of the arrhythmia Episodes may occur with sleep or with exercise
Diagnosis:
Electrocardiogram
- absence of P waves
- unorganized electrical activity in their place
- irregularity of R-R interval due to irregular conduction of impulses to the ventricles
Causes:
- Arterial hypertension
- Mitral valve disease (e.g. due to rheumatic heart disease or mitral valve prolapse)
- Heart surgery
- Coronary heart disease
- Excessive alcohol consumption ("binge drinking" or "holiday heart")
- Hyperthyroidism
- Hyperstimulation of the vagus nerve, usually by having large meals
Treatment
Rate control by
Beta blockers (e.g. metoprolol)
Digoxin
Calcium channel blockers (e.g. verapamil)
Rhythm control
Electrical cardioverion by application of a DC electrical shock
Chemical cardioversion is performed with drugs eg amiodarone
Radiofrequency ablation : uses radiofrequency energy to destroy abnormal electrical pathways in heart tissue It is used in recurrent AF
In confirmed AF, anticoagulant treatment is a crucial way to prevent stroke
Atrial flutter
Atrial flutter is a regular, rhythmic tachycardia originating in the atria. The rate in the atria is over 220 beats/minute, and typically about 300 beats/minute
he morphology on the surface EKG is typically a sawtooth pattern.
The ventricles do not beat as fast as the atria in atrial flutter
Supraventricular tachycardia
apid rhythm of the heart in which the origin of the electrical signal is either the atria or the AV node
it is important to determine whether a wide-complex tachycardia is an SVT or a ventricular tachycardia, since they are treated differently
Sick sinus syndrome : a group of abnormal heartbeats (arrhythmias) presumably caused by a malfunction of the sinus node, the heart's "natural" pacemaker.
Ventricular fibrillation
is a cardiac condition which consists of a lack of coordination of the contraction of the muscle tissue of the large chambers of the heart. The ventricular muscle twitches randomly, rather than contracting in unison, and so the ventricles fail to pump blood into the arteries and into systemic circulation.
Ventricular fibrillation is a medical emergency: if the arrhythmia continues for more than a few seconds, blood circulation will cease, as evidenced by lack of pulse, blood pressure and respiration, and death will occur. Ventricular fibrillation is a cause of cardiac arrest and sudden cardiac death