NEET MDS Lessons
General Pathology
Human immunodeficiency virus (HIV)
1. Part of the Retroviridae family (i.e., it is a retrovirus).
2. Basic virion structure
a. The nucleocapsid contains single stranded RNA and three enzymes: reverse transcriptase, integrase, and protease.
b. An exterior consists of two glycoproteins, gp120 and gp41, which are imbedded in the lipid bilayer. This lipid bilayer was obtained from the host cell via budding.
3. Virion characteristics
a. The HIV genome includes:
(1) gag gene—codes for core proteins.
(2) pol gene—codes for its three enzymes.
(3) env gene—codes for its two envelope glycoproteins.
b. HIV enzymes
(1) Reverse transcriptase—reverse transcription of RNA to viral DNA.
(2) Integrase—responsible for integrating viral DNA into host DNA.
(3) Protease—responsible for cleaving precursor proteins.
4. Pathogenicity
a. HIV mainly infects CD4 lymphocytes, or helper T cells. Its envelope protein, gp120, binds specifically with CD4 surface
receptors. After entry, viral RNA is transcribed by reverse transcriptase to viral DNA and integrated into the host DNA. New virions are synthesized and released by lysis of the host cell.
b. The predominant site of HIV replication is lymphoid tissues.
c. Although HIV mainly infects CD4 helper T cells, it can bind to any cell with a CD4 receptor, including macrophages, monocytes, lymph node dendritic cells, and a selected number of nerve cells. Macrophages are the first cells infected by HIV.
5. HIV infection versus acquired immunodeficiency syndrome (AIDS).
a. AIDS describes an HIV-infected person who has one of the following conditions:
(1) A CD4 lymphocyte count of less than 200.
(2) The person is infected with an opportunistic infection or other AIDS-defining illness, including (but not limited to) tuberculosis, recurrent pneumonia infections, or invasive cervical cancer.
b. The cause of death in an AIDS patient is most likely due to an opportunistic infection.
6. Common opportunistic infections associated with AIDS:
a. Pneumonia caused by Pneumocystis jiroveci (carinii).
b. Tuberculosis.
c. Periodontal disease—severe gingivitis, periodontitis, ANUG, necrotizing stomatitis.
d. Candidiasis.
e. Oral hairy leukoplakia (EBV).
f. Kaposi’s sarcoma (HHV-8).
g. Recurrent VZV infections.
h. Condyloma acuminatum or verruca vulgaris (warts, HPV)—less common.
i. CMV infections.
j. Disseminated herpes simplex, herpes zoster.
k. Hodgkin’s, non-Hodgkin’s lymphoma.
7. Laboratory diagnosis of HIV
a. ELISA test—detects HIV antibodies.
False negatives do occur.
b. Western blot—detects HIV proteins.
There is a 99% accuracy rate when both the ELISA test and Western blot are used to diagnose HIV infection.
c. PCR—more sensitive; can amplify and identify the virus at an early stage.
8. Treatment
a. Inhibitors of reverse transcriptase.
(1) Nucleoside analogs
(a) Inhibit viral replication via competitive inhibition.
(b) Examples: zidovudine (AZT), didanosine, lami- vudine, stavudine.
(2) Nonnucleoside inhibitors.
(a) Act by binding directly to reverse transcriptase.
(b) Examples: nevirapine, delavirdine.
b. Protease inhibitor.
c. “Triple cocktail” therapy—often consists of two nucleoside inhibitors and a protease inhibitor.
Cytopathologic techniques
Cytopathology is the study of cells from various body sites to determine the cause or nature of disease.
Applications of cytopathology:
- Screening for the early detection of asymptomatic cancer
2. Diagnosis of symptomatic cancer
3. Surveillance of patients treated for cancer
Cytopathologic methods
There are different cytopathologic methods including:
1. Fine-needle aspiration cytology (FNAC) -In FNAC, cells are obtained by aspirating the diseased organ using a very thin needle under negative pressure.
Superficial organs (e.g. thyroid, breast, lymph nodes, skin and soft tissues) can be easily aspirated.
Deep organs, such as the lung, mediastinum, liver, pancreas, kidney, adrenal gland, and retroperitoneum are aspirated with guidance by fluoroscopy, ultrasound or CT scan.
- Exfoliative cytology
Refers to the examination of cells that are shed spontaneously into body fluids or secretions. Examples include sputum, cerebrospinal fluid, urine, effusions in body cavities (pleura, pericardium, peritoneum), nipple discharge and vaginal discharge.
- Abrasive cytology
Refers to methods by which cells are dislodged by various tools from body surfaces (skin, mucous membranes, and serous membranes). E.g. preparation of cervical smears with a spatula or a small brush to detect cancer of the uterine cervix at early stages.
Huntington’s disease
a. Causes dementia.
b. Genetic transmission: autosomal dominant.
c. Characterized by the degeneration of striatal neurons, affecting cortical and basal ganglia function.
d. Clinically, the disease affects both movement and cognition and is ultimately fatal.
Viral meningitis
1. Can be caused by many different viruses, including cytomegalovirus, herpes virus, rabies, and HIV.
2. CSF fluid from a spinal tap differs from that seen in a bacterial infection. It shows mononuclear cells, higher levels of protein, and normal levels of glucose.
Glomerulonephritis
Characterized by inflammation of the glomerulus.
Clinical manifestations:
Nephrotic syndrome (nephrosis) → Most often caused by glomerulonephritis.
Laboratory findings:
(i) Proteinuria (albuminuria) and lipiduria—proteins and lipids are present in urine.
(ii) Hypoalbuminemia—decreased serum albumin due to albuminuria.
(iii) Hyperlipidemia—especially an increase in plasma levels of low-density lipoproteins and cholesterol.
Symptoms
severe edema, resulting from a decrease in colloid osmotic pressure due to a decrease in serum albumin.
Agranulocytosis. Severe neutropenia with symptoms of infective lesions.
Drugs. are an important cause and the effect may be due to .
-Direct toxic effect.
-Hypersensitivity.
Some of the 'high risk drugs are.
-Amidopyrine.
-Antithyroid drugs.
-Chlorpromazine, mapazine.
-Antimetabolites and other drugs causing pancytopenia.
Bloodpicture: Neutropenia with toxic granules in neutrophils. Marrow shows decrease in granulocyte precursors with toxic granules in them.
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.