NEET MDS Lessons
General Pathology
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
Summary
Hepatitis A → ssRNA → Picornavirus → Oral–anal
Hepatitis B → dsDNA → Hepadnavirus → Sexual contact , Blood (needles), Perinatal
Hepatitis C → ssRNA → Flavivirus → Sexual contact , Blood (needles)
Hepatitis D → ssRNA → Deltavirus → Sexual contact, Blood (needles)
Hepatitis E → ssRNA → Calicivirus → Oral–anal
Measles (rubeola)
-incubation period 7 to 14 days
-begins with fever (up to 40 degrees C), cough, conjunctivitis (photophobia is first sign), and coryza (excessive mucous production)Æfollowed by Koplik's spots (red with white center) in the mouth, posterior cervical Lymphadenopathy, and a generalized, blanching, maculopapular, brownish-pink rash (viral induced vasculitis) beginning at the hairline and extending down over the body which gradually resolves in 5 days with some desquamation.
Lymphangitis
is the acute inflammation due to bacterial infections spread into the lymphatics most common are group A β-hemolytic streptococci.
lymphatics are dilated and filled with an exudate of neutrophils and monocytes.
red, painful subcutaneous streaks (the inflamed lymphatics), with painful enlargement of the draining lymph nodes (acute lymphadenitis).
subsequent passage into the venous circulation can result in bacteremia or sepsis.
Cholecystitis
It is inflammation of the gall bladder. It may be acute or chronic.
In 80-90% of cases, it is associated with gall stones (Calcular cholecystis).
Causes and pathogenesis:-
Obstruction of cystic or common bile duct- By stones, strictures, pressure from the outside, tumors etc.
Obstruction , chemical irritation of the gall bladder, Secondary bacterial infection, stone formation, trauma to the wall of gall
bladder
Secondary bacterial infection
Usually by intestinal commensals E.coli, streptococcus fecalis. They reach the gall bladder by lymphatics.
S.typhi reaches the gall bladder after systemic infection
Acute cholecystitis
Gall bladder is enlarged edematous and fiery red in color.
- Wall is edematous, hyperemic, may show abscesses or gangrenous dark brown or green or black foci which may perforate.
Serous covering show fibrinosuppurative inflammation and exudation. Mucosa is edematous, hyperemic and ulcerated.
- If associated with stones, obstruction results in accumulation of pus leading to Empyaema of the gall bladder.
Fate:- Healing by fibrosis and adhesions.
Complications:-
- Pericholecystic abscess.
- Rupture leading to acute peritonitis.
- Ascending suppurative cholangitis and liver abscess
Chronic cholecystitis
May follow Acute cholecystitis or starts chronic. Gall stones are usually present.
Pathology
1. If associated with obstruction: Gall bladder is dilated. Wall may be thickened or thinned out. Contents may be clear, turbid or purulent.
2. If not associated with obstruction: - Gall bladder is contracted, wall is markedly thickened.
3. Serosa is smooth with fibrous adhesions. Draining lymph nodes are enlarged.
4. Wall is thickened, opaque and gray-white with red tinge.
5. Mucosa is gray- red with ulcerations and pouches.
6. Stones are usually present
Neuroblastoma and Related Neoplasms
Neuroblastoma is the second most common solid malignancy of childhood after brain tumors, accounting for up to10% of all pediatric neoplasms. They are most common during the first 5 years of life. Neuroblastomas may occur anywhere along the sympathetic nervous system and occasionally within the brain. Most neuroblastomas are sporadic. Spontaneous regression and spontaneous- or therapy-induced maturation are their unique features.
Gross features
- The adrenal medulla is the commonest site of neuroblastomas. The remainder occur along the sympathetic chain, mostly in the paravertebral region of the abdomen and posterior mediastinum.
- They range in size from minute nodules to large masses weighing more than 1 kg.
- Some tumors are delineated by a fibrous pseudo-capsule, but others invade surrounding structures, including the kidneys, renal vein, vena cava, and the aorta.
- Sectioning shows soft, gray-tan, brain-like tissue. Areas of necrosis, cystic softening, and hemorrhage may be present in large tumors.
Microscopic features
- Neuroblastomas are composed of small, primitive-appearing neuroblasts with dark nuclei & scant cytoplasm, g rowing in solid sheets.
- The background consists of light pinkish fibrillary material corresponding to neuritic processes of the primitive cells.
- Typically, rosettes can be found in which the tumor cells are concentrically arranged about a central space filled with the fibrillary neurites.
- Supporting features include include immunochemical detection of neuron-specific enolase and ultrastructural demonstration of small, membrane-bound, cytoplasmic catecholamine-containing secretory granules.
- Some neoplasms show signs of maturation, either spontaneous or therapy-induced. Larger ganglion-like cells having more abundant cytoplasm with large vesicular nuclei and prominent nucleoli may be found in tumors admixed with primitive neuroblasts (ganglioneuroblastoma). Further maturation leads to tumors containing many mature ganglion-like cells in the absence of residual neuroblasts (ganglioneuroma).
Many factors influence prognosis, but the most important are the stage of the tumor and the age of the patient. Children below 1 year of age have a much more favorable outlook than do older children at a comparable stage of disease.
Miscroscopic features are also an independent prognostic factor; evidence of gangliocytic differentiation is indicative of a "favorable" histology. Amplification of the MYCN oncogene in neuroblastomas is a molecular event that has profound impact on prognosis. The greater the number of copies, the worse is the prognosis. MYCN amplification is currently the most important genetic abnormality used in risk stratification of neuroblastic tumors.
About 90% of neuroblastomas produce catecholamines (as pheochromocytomas), which are an important diagnostic feature (i.e., elevated blood levels of catecholamines and elevated urine levels of catecholamine metabolites such as vanillylmandelic acid [VMA] and homovanillic acid [HVA]).
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