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PA31.1-10 | Endocrine System — PBL Case

CLINICAL SETTING

Dr Anitha, a 38-year-old assistant professor of biochemistry at a medical college in Puducherry, presents to the medicine OPD for a routine annual health check. She has been feeling 'generally unwell' for several months — fatigue that she attributed to academic workload, thirst, and frequent nocturnal urination. She takes no regular medications and has no known medical history. Her BMI is 32 kg/m², waist circumference 96 cm. Family history is significant: her father developed 'sugar disease' in his forties and lost vision in one eye; her younger brother developed Type 1 diabetes in adolescence and was rushed to hospital once in a coma. As the registrar prepares to examine her, another patient — Kumar, a 60-year-old man — is wheeled into the adjacent bay in acute distress, confused and moaning, brought by his wife from a nearby village. The nurse's notes state: 'long-standing known diabetic, on irregular medication, presented after vomiting and not eating for two days.'

Trigger 1: Anitha's Numbers

Anitha's fasting plasma glucose is 9.4 mmol/L. A repeat test two days later confirms 9.1 mmol/L. Her HbA1c is 7.8%. She has no ketonuria. Her C-peptide level is 1.8 nmol/L (normal range 0.36–1.17 nmol/L — elevated, indicating significant insulin secretion). GAD-65 and islet cell antibodies are both negative. Meanwhile, Kumar's initial blood gas shows pH 7.11, bicarbonate 8 mEq/L, blood glucose 34 mmol/L, and urine dipstick is 3+ for ketones. His serum potassium is 5.8 mEq/L despite clinical signs of dehydration.

DISCUSSION POINTS

Anitha's glucose and HbA1c meet criteria for diabetes mellitus. Using the ADA diagnostic criteria, confirm the diagnosis and classify her diabetes as Type 1 or Type 2, justifying your classification using C-peptide level, antibody status, age, and BMI.
Contrast the pathogenesis of Type 1 DM (autoimmune beta-cell destruction) with the two-hit mechanism of Type 2 DM (insulin resistance followed by beta-cell failure). What islet morphological changes are expected in each type?
Kumar presents with a pH of 7.11 and 3+ ketonuria. Diagnose his acute complication and explain its pathophysiology: why does absolute insulin deficiency lead to ketone body formation, Kussmaul breathing, and metabolic acidosis?
Kumar's potassium is 5.8 mEq/L despite clinical dehydration. Explain the 'potassium paradox' in DKA — why is serum potassium elevated at presentation while total body potassium is depleted — and what is the clinical management implication?

Click to reveal Trigger 2: Fifteen Years Later — The Silent Damage (discuss previous trigger first!)

Trigger 2: Fifteen Years Later — The Silent Damage

Anitha is counselled and started on metformin plus lifestyle intervention. She is lost to follow-up for 15 years. She returns at age 53, brought by her daughter, who noticed Anitha stumbling and has poor vision in both eyes. Review of records shows her HbA1c has been consistently above 9% for at least eight years. Her eGFR is 32 mL/min/1.73m² (CKD Stage 3b). Urine protein:creatinine ratio is 680 mg/mmol (severely elevated). Blood pressure is 168/104 mmHg. Fundoscopy reveals multiple flame haemorrhages, hard exudates, and two neovascular tufts on the left disc. Her feet show loss of vibration sense to the mid-shin bilaterally. A renal biopsy is performed to confirm the pathological diagnosis of the kidney disease.

DISCUSSION POINTS

Anitha's renal biopsy returns showing nodular deposits of PAS-positive material at the periphery of glomerular tufts, with thickened capillary basement membranes and arteriolar hyalinosis. Name this specific lesion, explain its pathogenesis from hyperglycaemia to advanced glycation end-products to basement membrane thickening, and state why it is the leading cause of end-stage renal disease in India.
Anitha has features of both non-proliferative and proliferative diabetic retinopathy. Explain the 'pericyte loss → microaneurysm → VEGF → neovascularisation' sequence, and state why proliferative retinopathy is vision-threatening while background retinopathy is not.
Explain the pathological basis of diabetic peripheral neuropathy at the Schwann cell and axonal level. What is the shared biochemical mechanism (polyol pathway, AGEs, oxidative stress) that underlies microangiopathy, nephropathy, retinopathy, and neuropathy?
Anitha's cardiovascular risk is markedly elevated. What macrovascular complication pathway links diabetes mellitus to accelerated atherosclerosis, and which vessel territories are most commonly and most severely affected in diabetic patients compared with non-diabetics?

Click to reveal Trigger 3: The Ward Next Door — Three Endocrine Puzzles (discuss previous trigger first!)

Trigger 3: The Ward Next Door — Three Endocrine Puzzles

The nephrology ward receives two more patients the same week. The first is Prakash, a 48-year-old man with fatigue, weight loss of 9 kg over three months, progressive constipation, polyuria, and a serum calcium of 3.2 mmol/L. His intact PTH is 210 pg/mL (markedly elevated). A neck ultrasound shows a 2.2 cm hypervascular nodule in the inferior left parathyroid gland. X-rays of his hands reveal subperiosteal erosion of the radial aspect of the middle phalanges. The second patient, Kavitha, a 40-year-old woman, is admitted with progressive weight gain, central obesity, easy bruising, purple abdominal striae, and resistant hypertension. Her morning cortisol is 980 nmol/L; ACTH is elevated; low-dose dexamethasone fails to suppress cortisol; high-dose dexamethasone suppresses cortisol by 62%. A third patient — an emaciated 60-year-old man with painless jaundice, Courvoisier's sign, and recent new-onset diabetes — is admitted from the surgical team.

DISCUSSION POINTS

Prakash has hypercalcaemia + markedly elevated PTH + a parathyroid nodule. Diagnose his condition and explain the pathological mechanism by which PTH causes subperiosteal bone resorption, renal stones, and the classic symptoms encoded in 'Stones, Bones, Groans, and Psychic Moans.'
Kavitha's high-dose dexamethasone suppresses cortisol by >50%, distinguishing her from ectopic ACTH syndrome. Construct the diagnostic algorithm for Cushing syndrome: first distinguish exogenous from endogenous (ACTH level), then distinguish pituitary Cushing disease from ectopic ACTH (high-dose dexamethasone suppression test) and from adrenal adenoma (bilateral vs unilateral adrenal morphology).
The emaciated man with painless jaundice, Courvoisier's sign, and new-onset diabetes almost certainly has a carcinoma of the head of the pancreas. Explain why head-of-pancreas cancers present with jaundice and why new-onset diabetes may be a paraneoplastic phenomenon. What is the molecular precursor sequence (PanIN grades with KRAS mutation) and the characteristic desmoplastic histology?
Contrast the pathogenesis of primary, secondary, and tertiary hyperparathyroidism. In which clinical context is secondary hyperparathyroidism encountered most commonly in India, and what is the calcium-phosphate-PTH axis dysregulation in CKD?

Group Task Assignments

Group 1: Diabetes mellitus — classification, pathogenesis, and morphology

Construct a comparison chart of Type 1 DM vs Type 2 DM covering: age of onset, mechanism, HLA association, antibodies, C-peptide, islet morphology (insulitis vs amyloid/IAPP deposition), acute complication, and long-term treatment.
Draw the 'metabolic clock' of Type 2 DM: from insulin resistance (adiposity, reduced GLUT4) → compensatory hyperinsulinaemia → progressive beta-cell exhaustion → overt diabetes → chronic complications.

Competencies: PA31.5

Group 2: Diabetic chronic complications — pathological basis

Illustrate the pathological sequence from hyperglycaemia to Kimmelstiel-Wilson nodules: AGE formation → basement membrane thickening → podocyte loss → mesangial expansion → nodular glomerulosclerosis.
Prepare a systems-level map of all chronic diabetic complications linking the shared pathophysiological mechanism (polyol pathway overactivity, AGE accumulation, PKC activation, oxidative stress) to each end-organ (kidney, retina, nerve, heart, vessels).

Competencies: PA31.5

Group 3: Thyroid pathology — goitre, thyroiditis, and function disorders

Classify thyroid swellings by functional status and pathological type; for each type give: TSH level, T3/T4 level, RAIU result, and the diagnostic discriminator that separates it from Graves disease.
Compare the morphology and clinical course of Hashimoto thyroiditis (hypothyroid, autoimmune), Graves disease (hyperthyroid, autoimmune), and subacute granulomatous thyroiditis (de Quervain — transient hyperthyroid then hypothyroid).

Competencies: PA31.1, PA31.2, PA31.3

Group 4: Adrenal disorders — Cushing syndrome, Addison disease, and pheochromocytoma

Draw the Cushing syndrome algorithm from clinical suspicion → biochemical confirmation (24h urine cortisol / overnight DST) → ACTH-dependent vs independent → pituitary vs ectopic vs adrenal → imaging.
Prepare a comparison card for primary adrenal insufficiency (Addison disease) vs secondary adrenal insufficiency, focusing on: ACTH level, electrolytes, pigmentation, cause, and adrenal morphology (autoimmune atrophy vs bilateral haemorrhage in Waterhouse-Friderichsen).

Competencies: PA31.8, PA31.9, PA31.10

Group 5: Thyroid tumours and hyperparathyroidism

Construct the four-tumour thyroid carcinoma comparison table: papillary (BRAF/RET, Orphan Annie nuclei, psammoma bodies, lymphatics), follicular (capsular/vascular invasion, haematogenous, RAS/PAX8-PPARG), medullary (calcitonin, amyloid, RET/MEN2A), and anaplastic (pleomorphic giant cells, lethal).
Explain the pathogenesis of primary hyperparathyroidism (parathyroid adenoma in 85% of cases) and map its clinical manifestations to the PTH-calcium-phosphate axis, including the significance of subperiosteal resorption on hand X-ray as a pathognomonic finding.

Competencies: PA31.4, PA31.6

Learning Issues

Research these questions and bring your findings to the discussion.

[PA31.1] How are thyroid swellings classified by function and pathology, what is the role of iodine deficiency in diffuse and multinodular goitre, and what are the gross and microscopic features of each goitre type?
[PA31.2] What is the pathogenesis of Graves disease (TSI antibody mechanism, TSHR activation, diffuse hyperplasia), and how does the RAIU pattern distinguish it from thyroiditis-associated thyrotoxicosis?
[PA31.3] What are the causes, clinical features, and laboratory patterns of thyrotoxicosis versus hypothyroidism, and how does Hashimoto thyroiditis produce hypothyroidism through autoimmune mechanisms?
[PA31.4] What are the epidemiology, etiology, pathology, nuclear features (for PTC), invasion criteria (for FTC), calcitonin/amyloid profile (for MTC), and prognosis of the four major thyroid carcinomas?
[PA31.5] What are the classification, pathogenesis, islet morphology, acute complications (DKA vs HHS), and chronic microvascular and macrovascular complications of diabetes mellitus, including the pathological basis of the Kimmelstiel-Wilson nodule?
[PA31.6] What is the pathogenesis and cause distribution of primary hyperparathyroidism, and how do elevated PTH levels produce hypercalcaemia, renal stones, subperiosteal bone resorption, and the other classical manifestations?
[PA31.7] What are the risk factors, molecular precursor sequence (PanIN and KRAS), desmoplastic histology, clinical presentations (head vs body/tail), CA 19-9 marker, and the dismal prognosis of pancreatic ductal adenocarcinoma?
[PA31.8] What are the causes of primary and secondary adrenal insufficiency, what is the mechanism of hyperpigmentation that distinguishes primary from secondary disease, and what adrenal morphological findings characterise autoimmune Addison disease?
[PA31.9] What is the clinical and biochemical algorithm for diagnosing and localising the cause of Cushing syndrome, and what adrenal morphological appearances correspond to each aetiology (bilateral hyperplasia vs adenoma vs carcinoma)?
[PA31.10] What are the pathological features, 'Rule of 10s,' clinical presentation (paroxysmal hypertension), catecholamine markers, and malignancy criteria of pheochromocytoma and neuroblastoma?