Make answers from all the main topic that i can read here and write in muhs exam 2nd year pathology mbbs in easy language
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Here are all 5 complete MUHS exam answers written from your PDF in easy, exam-ready language:
MUHS 2nd Year Pathology - Exam Answers
(From Johari Pathology - Thyroid & Skin)
TOPIC 1: HASHIMOTO'S THYROIDITIS
Q. Describe the pathogenesis, morphology and clinical features of Hashimoto's thyroiditis.
Definition: Chronic lymphocytic (Hashimoto's) thyroiditis is an autoimmune disease causing gradual failure of thyroid function. It is the most common cause of hypothyroidism in iodine-sufficient areas.
Epidemiology: Age 45-65 years. Females >> Males (F:M = 10-20:1)
Etiology: Genetic association with CTLA4 and PTPN22 gene polymorphisms. Circulating antithyroid antibodies are found even in asymptomatic relatives.
PATHOGENESIS (3 steps):
-
Failure of self-tolerance - Due to genetic factors, T-regulatory cells fail to protect thyroid antigens. Abnormal exposure of thyroid antigens initiates the process.
-
Induction of autoimmunity - Circulating autoantibodies form against thyroglobulin and thyroid peroxidase (TPO)
-
Progressive destruction of thyrocytes via 3 mechanisms:
- CD8+ cytotoxic T-cells kill thyroid epithelium directly
- CD4+ T-cells activate macrophages → cytokine-mediated injury
- Antithyroid antibodies + NK cells → antibody-dependent cytotoxicity
Result: Thyroid parenchyma replaced by fibrosis → Hypothyroidism
MORPHOLOGY:
Gross:
- Diffuse symmetric enlargement, firm, nodular
- Capsule intact, well-demarcated
- Cut surface: Pale gray-tan, accentuated lobulation
Microscopy:
- Inflammation - Dense lymphocytic + plasma cell infiltrate; lymphoid follicles with germinal centers
- Epithelial changes - Follicular atrophy + Hurthle cell (Askanazy cell) metaplasia - cells have abundant eosinophilic granular cytoplasm
Clinical: Goiter, hypothyroidism (weight gain, fatigue, cold intolerance); positive anti-TPO antibodies; increased risk of thyroid lymphoma.
TOPIC 2: THYROID CARCINOMA
Q. Classify and compare the types of thyroid carcinoma.
| Feature | Papillary (75-80%) | Follicular (10-20%) | Medullary (5-7%) | Anaplastic (Rarest) |
|---|---|---|---|---|
| Cell of Origin | Follicular cell | Follicular cell | Parafollicular (C) cell | Follicular cell |
| Mutation | RET | RAS | RET | P53 |
| Key Micro | Ground glass nuclei, Psammoma bodies, nuclear grooves | Follicles, no papillae | Amyloid in stroma, calcitonin | Spindle + giant cells |
| Prognosis | Good | Good | Intermediate | Worst |
Papillary Ca - Key Features (Most asked):
- Nuclei: Orphan Annie eye / Ground glass appearance - transparent, empty-looking nuclei
- Nuclear grooves and inclusion bodies
- Psammoma bodies (concentric calcified spherules)
- Fibrovascular papillae covered by single layer of tumor cells
Medullary Ca - Key Features:
- Nests of cells separated by fibrous septa
- Amyloid deposits in stroma (diagnostic)
- Secretes calcitonin (tumor marker)
TOPIC 3: SQUAMOUS CELL CARCINOMA OF SKIN
Q. Describe etiology, pathogenesis and morphology of SCC skin.
Definition: Second most common skin tumor, arising on sun-exposed sites. More common in men.
Risk Factors: UV light (DNA damage), chronic immunosuppression, tars/oils, chronic non-healing ulcers, burn scars, ionizing radiation, tobacco and betel nut.
Pathogenesis: Mutated TP53 → loss of DNA repair; dysregulated RAS signaling → uncontrolled proliferation.
Clinical: Sharply defined red scaling plaques (in situ) → nodular ulcerating growth with elevated, indurated border (invasive).
MORPHOLOGY:
Gross: Nodular ulcerated lesion, everted margins, hard indurated border.
Microscopy (by grade):
- Well-differentiated: Polygonal squamous cells in orderly lobules, large keratin production, squamous/epithelial keratin pearls - most characteristic, intercellular bridges (desmosomes)
- Moderately differentiated: Anaplastic cells, single-cell keratinization (dyskeratosis)
- Poorly differentiated: Minimal keratin, needs IHC for keratins to confirm
TOPIC 4: MELANOMA
Q. Describe the etiology, pathogenesis, morphology and clinical features of Melanoma.
Definition: Malignant tumor of melanocytes. Sites: Trunk, leg, face, sole, palm, nail beds.
Etiology: Primarily sun exposure (UV radiation). Lightly pigmented individuals at greater risk.
Pathogenesis:
- Tumor suppressor mutations: CDKN2A locus (encodes p15/INK4b, p16/INK4a, p14/ARF) → increased melanocyte proliferation; RB gene mutations
- Oncogene activation: Mutations in RAS or BRAF → activate RAS/RAF/MAP kinase pathway → cell proliferation and survival
MORPHOLOGY - Two Growth Phases:
| Radial (Initial) | Vertical (Later) | |
|---|---|---|
| Direction | Horizontal spread in epidermis + superficial dermis | Downward invasion into deep dermis |
| Metastasis | Cannot metastasize | Can metastasize |
| Prognosis | Good | Depends on Breslow thickness (depth of invasion) |
Microscopy:
- Tumor cells larger than normal melanocytes
- Nuclei: Large, irregular contours, prominent red (eosinophilic) nucleoli, mitoses
- Melanin pigment - uniform brown fine granules in cytoplasm
- Tumor Infiltrating Lymphocytes (TILs) around the tumor
ABCD Warning Signs (Clinical):
- A - Asymmetry
- B - Irregular Borders
- C - Variegated Color (black, brown, red, gray, blue)
- D - Diameter >6-10 mm
TOPIC 5: OSTEOSARCOMA
Q. Describe the pathogenesis, morphology, clinical course and radiological features of Osteosarcoma.
Definition: Highly malignant bone tumor characterized by production of osteoid (unmineralized bone) or bone by malignant tumor cells.
Epidemiology: Age 10-20 years (primary); >40 years (secondary). Boys > Girls (2:1).
Pathogenesis:
- Primary OS (young): Mutations in RB gene (retinoblastoma gene) + TP53; MDM2 and CDK4 overexpressed
- Secondary OS (elderly): Pre-existing bone disease (Paget's) or previous alkylating chemotherapy
Sites: Metaphysis of long bones - Lower femur > Upper tibia > Proximal humerus (near knee/shoulder)
MORPHOLOGY:
Gross: Big bulky tumor; cut surface gray-white, gritty; areas of hemorrhage and cystic degeneration.
Microscopy:
- Osteoid production by malignant cells = SINGLE DIAGNOSTIC FEATURE
- Osteoid appears as: Dense, uniform, eosinophilic, glassy intercellular material
- Malignant cells: pleomorphic, large hyperchromatic nuclei, frequent mitoses
- Bizarre tumor giant cells common
Clinical: Painful, progressively enlarging mass near knee/shoulder; swollen + tender; reduced joint function; serum alkaline phosphatase raised.
Radiology (X-ray) - Two Classic Signs:
- Codman Triangle - Periosteum lifted by tumor → triangular shadow between cortex and lifted periosteum
- Sunburst Appearance - Tumor extends to soft tissue → parallel mineral lines in periosteum look like sun rays
QUICK REVISION - KEY IDENTIFIERS
| Disease | One-Line Identifier |
|---|---|
| Hashimoto's | Hurthle cells + lymphoid follicles with germinal centers |
| Papillary Ca | Orphan Annie eye nuclei + Psammoma bodies + nuclear grooves |
| Medullary Ca | Amyloid in stroma + calcitonin secretion |
| SCC Skin | Keratin pearls + intercellular bridges |
| Melanoma | ABCD + radial then vertical growth + prominent nucleoli |
| Osteosarcoma | Osteoid by malignant cells + Codman triangle + sunburst on X-ray |
Exam Structure tip: Always write in this order - Definition → Etiology → Pathogenesis → Morphology (Gross then Microscopy) → Clinical Features. This is how MUHS awards full marks.
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