NEET MDS Lessons
General Pathology
Muscle pathology
1. Myasthenia gravis
a. An autoimmune disease caused by autoantibodies to acetylcholine receptors at the neuromuscular junctions.
b. Characterized by muscle weakness or the inability to maintain long durations of muscle contractions; this worsens during exercise but recovers after rest.
c. Affects various muscle groups, including:
(1) Eyes—diplopia, ptosis.
(2) Neck—dysphagia, problems swallowing or speaking.
(3) Extremities—arms and legs.
d. Treatment: cholinesterase inhibitors(neostigmine), anti-immune therapy.
2. Muscle tumors
a. Rhabdomyoma—benign tumor of skeletal muscle.
b. Leiomyoma
(1) Benign tumor of smooth muscle.
(2) Most common tumor found in women.
(3) Usually affects the uterus, although it can occur anywhere.
c. Rhabdomyosarcoma
(1) Malignant tumor of skeletal muscle.
(2) Most common sarcoma found in children.
(3) Usually affects head and neck region—orbit, nasal cavity, and nasopharynx.
Psoriasis is a chronic disorder characterized by scaly, erythematous plaques, which histologically are secondary to epidermal proliferation.
- genetic factors (HLA relationships), environmental (physical injury, infection, drugs, photosensitivity), abnormal cellular proliferation (deregulation of epidermal proliferation) and microcirculatory changes in the papillary dermis (diapedesis of neutrophils into the epidermis) are all interrelated.
- the plaques of psoriasis are characteristically well-demarcated pink or salmon colored lesions covered by a loosely-adherent silver-white scale which, when picked off, reveals pinpoint bleeding sites (Auspitz sign).
- the nail changes in psoriasis include pitting, dimpling, thickening and crumbling with a yellowish-brown discoloration of the nail plate.
- the characteristic histologic features of psoriasis include:
- hyperkeratosis
- absence of the granulosa cells (present in lichen planus).
- parakeratosis
- regular, club-shaped elongation of the rete pegs (irregular and saw toothed in lichen planus) with vessel proliferation in the papillary dermis (reason for the bleeding associated with Auspitz sign).
- characteristic subcorneal collection of neutrophils called a Munro's microabscess (diapedesis from vessels in papillary dermi).
- 7% develop HLA B27 positive psoriatic arthritis
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.
FUNGAL INFECTION
Mucormycosis (Zygomycosis; Phycomycosis)
Infection with tissue invasion by broad, nonseptate, irregularly shaped hyphae of diverse fungal species, including Rhizopus, Rhizomucor, Absidia, and Basidiobolus.
Infection is most common in immunosuppressed persons, in patients with poorly controlled diabetes, and in patients receiving the iron-chelating drug desferrioxamine.
Symptoms and Signs
Rhinocerebral mucormycosis is the most common form, but primary cutaneous, pulmonary, or GI lesions sometimes develop, and hematogenous dissemination to other sites can occur. Rhinocerebral infections are usually fulminant and frequently fatal. Necrotic lesions usually appear on the nasal mucosa or sometimes the palate.
Eosinophilia:
Causes
-Allergic disorders.
-Parasitic infection.
-Skin diseases.
-Pulmonary eosinophilia.
-Myeloproliferative lesions and Hodgkin's disease.
IMMUNO PATHOLOGY
Abnormalities of immune reactions are of 3 main groups
- Hypersensitivity,
- Immuno deficiency,
- Auto immunity.
Hypersensitivity (ALLERGY)
This is an exaggerated or altered immune response resulting in adverse effects
They are classified into 4 main types.
I. Type I-(reaginic, anaphylactic). This is mediated by cytophylic Ig E antibodies, which get bound to mast cells. On re-exposure, the Ag-Ab reaction occurs on the mast cell surface releasing histamine.
Clinical situations
I. Systemic anaphylaxis, presenting with bronchospasm oedema hypertension, and even death.
2. Local (atopic) allergy.
- Allergic rhinitis (hay fever)
- Asthma
- Urticaria.
- Food allergies.
2. Type II. (cytotoxic). Antibody combines with antigen present on-cell surface. The antigen may be naturally present on the surface or an extrinsic substance (e.g.drug) attached to cell surface.
The cell is then destroyed by complement mediated lysis (C89) or phagocytosis of the antibody coated cell.
Clinical situations
- Haemolytic anemia.
- Transfusion reaction
- Auto immune haemolytic anemia.
- Haemolysis due to some drugs like Alpha methyl dopa
2. Drug induced thrombocytopenia (especially sedormid).
3 Agranulocytosis due to sensitivity to some drugs.
4 Goodpasture’s syndrome-glomermerulonephritis due to anti basement membrane antibodies.
3. Type III. (Immune complex disease). Circulating immune complexes especially small soluble complexes tend to deposit in tissues especially kidney, joints, heart and arteries.
These then cause clumping of platelets with subsequent release of histamine. and serotonin resulting in increased permeability. Also, complement activation occurs which being chemotactic results in aggregation of polymorphs and necrotising vasculitis due to release of lysosmal enzymes
Clinical situations
- Serum sickness.
- Immune complex glomerulonephritis.
- Systemic lupus erythematosus.
- Allergic alveolitis.
- Immune based vasculitis like
o Drug induced vasculitis.
o Henoch – Schonlein purpura
4. Type IV. (Cell mediated). The sensitized lymphocytes may cause damage by cytotoxicity or by lymphokines and secondarily involving macrophages in the reaction.
Clinical situations
I. Caseation necrosis in tuberculosis.
2. Contact dermatitis to
- Metals.
- Rubber.
- Drugs (topical).
- Dinitrochlorbenzene (DNCB).
5. Type V. (stimulatory) This is classed by some workers separately and by other with cytotoxic type (Type II) with a stimulatory instead of toxic effect
Clinical Situations :
LATS (long acting thyroid stimulator) results in thyrotoxicosis (Grave’s disease)
G-6 PD Deficiency
Occurs in Negroes, Mediterranean races, India and far East. It confers a protection Against falciparum malaria.
It is transmitted as X-linked trait of intermediate dominance (variable effect in homozygous females).
Haemolysis may be induced by :
• Primaquin and other anti malarials.
• Other drugs like chloramphenicol , analgesics, antitubercular drugs etc.
• Infections.
• Ingestion of Vicia faba bean (favism).
• Diabetic acidosis