NEET MDS Lessons
General Pathology
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.
Myocardial infarction (MI)—heart attack
A. Ischemia versus MI: Ischemia is a reversible mismatch between the supply and demand of oxygen. Infarction
is an irreversible mismatch that results in cell death caused by the lack of blood flow (oxygenation). For instance, chest pain caused by ischemia can be relieved by administering nitroglycerin (a vasodilator) to the patient. If the patient has an MI, the pain will not be relieved with nitroglycerin.
1. MIs most commonly occur when a coronary artery is occluded by a thrombus generated in an atherosclerotic artery.
2. Symptoms include:
a. Chest pain, shortness of breath.
b. Diaphoresis (sweating), clammy hands.
c. Nausea, vomiting.
3. Consequences:
a. Death (one third of patients).
b. Arrhythmias (most common immediate cause of death).
c. Congestive heart failure.
d. Myocardial rupture, which may result in death from cardiac tamponade.
e. Thrombus formation on infarcted tissue; may result in systemic embolism.
Mycobacterium leprae
- tuberculoid type has intact cellular immunity
- forms granulomas and kill the organisms (very few present).
- evokes a positive lepromin skin test
- localized skin lesions that lack symmetry
- nerve involvement (organisms invade Schwann cells) that dominates the clinical picture and leads to skin anesthesia, muscle atrophy and autoamputation.
- lepromatous leprosy patients lack cellular immunity
- no granulomas
- organisms readily identified
- negative lepromin skin test
- Bacteremia disseminates to cooler areas like the digits.
- symmetrical, skin lesions that produce the classic leonine facies; biopsy reveals grentz zone in superficial dermis and then organisms in macrophages.
- neural involvement is a late feature of the disease.
- lepromin skin test is to determine host immunity; not a diagnostic test.
- treatment: dapsone + rifampin
Polycystic kidney disease
Characterized by the formation of cysts and partial replacement of renal parenchyma.
Genetic transmission: autosomal dominant.
Clinical manifestations:
hypertension, hematuria, palpable renal masses, and progression to renal failure. Commonly associated with berry
aneurysms.
Pulmonary edema
Pulmonary edema is swelling and/or fluid accumulation in the lungs. It leads to impaired gas exchange and may cause respiratory failure.
Signs and symptoms
Symptoms of pulmonary edema include difficulty breathing, coughing up blood, excessive sweating, anxiety and pale skin. If left untreated, it can lead to death, generally due to its main complication of acute respiratory distress syndrome.
Diagnosis
physical examination: end-inspiratory crackles during auscultation (listening to the breathing through a stethoscope) can be due to pulmonary edema. The diagnosis is confirmed on X-ray of the lungs, which shows increased vascular filling and fluid in the alveolar walls.
Low oxygen saturation and disturbed arterial blood gas readings may strengthen the diagnosis
Causes
Cardiogenic causes:
- Heart failure
- Tachy- or bradyarrhythmias
- Severe heart attack
- Hypertensive crisis
- Excess body fluids, e.g. from kidney failure
- Pericardial effusion with tamponade
Non-cardiogenic causes, or ARDS (acute respiratory distress syndrome):
- Inhalation of toxic gases
- Multiple blood transfusions
- Severe infection
- Pulmonary contusion, i.e. high-energy trauma
- Multitrauma, i.e. severe car accident
- Neurogenic, i.e. cerebrovascular accident (CVA)
- Aspiration, i.e. gastric fluid or in case of drowning
- Certain types of medication
- Upper airway obstruction
- Reexpansion, i.e. postpneumonectomy or large volume thoracentesis
- Reperfusion injury, i.e. postpulmonary thromboendartectomy or lung transplantation
- Lack of proper altitude acclimatization.
Treatment
When circulatory causes have led to pulmonary edema, treatment with loop diuretics, such as furosemide or bumetanide, is the mainstay of therapy. Secondly, one can start with noninvasive ventilation. Other useful treatments include glyceryl trinitrate, CPAP and oxygen.
SMALL INTESTINE
Congenital anomalies
1. Meckel's diverticulum (a true diverticulum) is due to persistence of the omphalomesenteric vitelline duct.
2. Atresia is a congenital absence of a region of bowel, leaving a blind pouch or solid fibrous cord.
3. Stenosis refers to a narrowing of any region of the gastrointestinal tract, which may cause obstruction.
4. Duodenal diverticula are areas of congenital weakness permitting saccular enlargement. The duodenum is the most common region of the small bowel to contain diverticula.
5. Diverticula of jejunum and ileum are herniations of mucosa and submucosa at points where the mesenteric vessels and nerves enter.
Infections
1. Bacterial enterocolitis may be caused by the ingestion of preformed bacterial toxins, producing symptoms ranging from severe but transient nausea, vomiting, and diarrhea (Staphylococcus aureus toxin) to lethal paralysis (Clostridium botulinum toxin). Ingestion of toxigenic bacteria with colonization of the gut (e.g., Vibrio cholera, toxigenic E. coli, various species of Campylobacter jejuni, Shigella, salmonel
Yersinia, and many others) is another potential cause.
2. Nonbacterial gastroenterocolitis
a. Viral
(1) Rotavirus (children)
(2) Parvovirus (adults)
b. Fungal-Candida
c. Parasitic
(1 ) Entamoeba histolytica
(2) Giardia lamblia
3. In HIV patients. Causes of infectious diarrhea in HIV patients include Cryptosporidium, Microsporidia, isospora belli, CMV, and M. avium-intracellulare.
C. Malabsorption is defined as impaired intestinal absorption of dietary constituents.
Clinical features include diarrhea,steatorrhea, weakness, lassitude, and weight loss. Steatorrhea results in deficiency of fat-soluble vitamins (A, D, E, K) and calcium.
1. Celiac sprue
a. Etiology. Celiac sprue (nontropical sprue or gluten enteropathy) is caused by an allergic, immunologic, or toxic reaction to the gliadin component of gluten. There is a genetic predisposition.
Symptoms:
– Steatorrhea, abdominal distention, flatulence, fatigue, and weight loss
Complications:
– Iron and vitamin deficiency
– Risk of lymphoma (T-cell type)
Extraintestinal manifestation:
– Dermatitis herpetiformis (a pruritic papulovesicular rash with IgA deposits at the dermoepidermal junction)
2. Tropical sprue
Etiology. Tropical sprue is of unknown etiology, but may be caused by enterotoxigenic E. coli.
3. Disaccharidase deficiency is due to a deficiency of brush border enzymes. Lactase deficiency is most common.
4. Diverticulosis Coli
- Acquired colonic diverticula are present in nearly half of the population over the age of 50
- Diverticula are associated with low-fiber, low-residue diets
- Etiology is most likely high intraluminal pressure required for propulsion of hard, small stools
- Complications include hemorrhage, acute diverticulitis, perforation, fistula formation
Obstructive lesions
Hernias cause 15% of small intestinal obstruction. They are due to a protrusion of a serosa-lined sac through a weakness in the wall of the peritoneal cavity. They occur most commonly at the inguinal and femoral canals, at the umbilicus, and with scars. They may lead to entrapment, incarceration, and strangulation of the bowel.
Tumors of the small bowel account for only 5% of gastrointestinal tumors.
Benign tumors in descending order of frequency include:
leiomyomas, lipomas, adenomas (polyps), angiomas, and fibromas. Adenomatous polyps are most common in the stomach and duodenum and may be single or multiple, sessile or pedunculated. The larger the polyp, the greater the incidence of malignant transformation.
Malignant tumors, in descending order of frequency, include: endocrine cell tumors, lymphomas, adenocarcinomas, and leiomyosarcomas.
Idiopathic Inflammatory Bowel Disease (IBD)
- Chronic, relapsing, idiopathic inflamamtory disease of the GI tract
Crohn’s Disease
– Transmural granulomatous disease affecting any portion of the GI tract
Ulcerative Colitis
– Superficial, non-granulomatous inflammatory disease restricted to the colon
Ulcerative Colitis
- Bloody mucoid diarrhea, rarely toxic megacolon
- Can begin at any age, peaks at 20-25 years
- Annual incidence of ~10 per 100,000 in US
- Negligible risk of cancer in the first 10 years, but 1% per year risk of cancer thereafter
- Good response to total colectomy if medical therapy fails
Macroscopic
- Normal serosa
- Bowel normal thickness
- Continuous disease
- Confluent mucosal ulceration
- Pseudopolyp formation
Microscopic
- Crypt distortion + shortening
- Paneth cell metaplasia
- Diffuse mucosal inflammation
- Crypt abscesses
- Mucin depletion
- Mucosal ulceration
Crohn’s Disease
- Variable and elusive clinical presentation with diarrhea, pain, weight loss, anorexia, fever
- Can begin at any age, peaks at 15-25 years
- Annual incidence of ~3 per 100,000 in US
- Many GI complications and extracolonic manifestations
- Risk of cancer less than in UC
- Poor response to surgery
Macroscopic
Fat wrapping
Thickened bowel wall
Skip Lesions
Stricture formation
Cobblestoned mucosa
Ulceration
Microscopic
- Cryptitis and crypt abscesses
- Transmural inflammation
- Lymphoid aggregates +/- granulomas
- “Crohn’s rosary”
- Fissuring
- Neuromuscular hyperplasia
Respiratory Viral Diseases
Respiratory viral infections cause acute local and systemic illnesses. The common cold, influenza, pharyngitis, laryngitis (including croup), and tracheobronchitis are common.
An acute, usually afebrile, viral infection of the respiratory tract, with inflammation in any or all airways, including the nose, paranasal sinuses, throat, larynx, and sometimes the trachea and bronchi.
Etiology and Epidemiology
Picornaviruses, especially rhinoviruses and certain echoviruses and coxsackieviruses, cause the common cold. About 30 to 50% of all colds are caused by one of the > 100 serotypes of rhinoviruses.
Symptoms and Signs
Clinical symptoms and signs are nonspecific.
After an incubation period of 24 to 72 h, onset is abrupt, with a burning sensation in the nose or throat, followed by sneezing, rhinorrhea, and malaise.
Characteristically, fever is not present, particularly with a rhinovirus or coronavirus. Pharyngitis usually develops early; laryngitis and tracheobronchitis vary by person and causative agent. Nasal secretions are watery and profuse during the first days, but become more mucoid and purulent.
Cough is usually mild but often lasts into the 2nd wk.