A middle aged woman complains of gradual weight loss, fatigue and frequent micturition since last six months. Her fasting and post-prandial blood glucose levels were 180mg/dl and 300mg/dl respectively. i) What is the probable diagnosis? ii) Explain the symptoms of this patient. iii) Justify the beneficial role of regular exercise in this patient. iv) Enumerate the hormones synthesized from the endocrine pancreas.1+7+4+3
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Clinical Case Analysis: Probable Diagnosis - Type 2 Diabetes Mellitus
i) Probable Diagnosis (1 mark)
Type 2 Diabetes Mellitus (T2DM)
The diagnosis is supported by:
- Middle-aged woman (typical demographic for T2DM)
- Fasting blood glucose = 180 mg/dL (normal: <100 mg/dL; diagnostic threshold for DM: ≥126 mg/dL)
- Post-prandial (2-hr) blood glucose = 300 mg/dL (diagnostic threshold: ≥200 mg/dL)
- Classic triad of symptoms over 6 months
ii) Explanation of Symptoms (7 marks)
The patient's three cardinal symptoms - weight loss, fatigue, and frequent micturition (polyuria) - are all direct biochemical consequences of hyperglycemia.
1. Frequent Micturition (Polyuria)
In diabetes, blood glucose rises above the renal tubular threshold (~180 mg/dL). The renal tubules are unable to reabsorb all the filtered glucose, so glucose spills into the urine (glucosuria). This dissolved glucose in the tubular lumen exerts an osmotic effect, preventing water reabsorption - a mechanism called osmotic diuresis. The result is a large volume of urine (polyuria) and, consequently, increased thirst (polydipsia).
As Basic Medical Biochemistry explains: "Because of the osmotic diuretic effect of hyperglycemia, the kidney produces more urine, leading to dehydration, which, in turn, may lead to even higher levels of blood glucose." - Basic Medical Biochemistry: A Clinical Approach, 6e
2. Weight Loss (despite adequate or increased appetite)
In T2DM with insufficient insulin action, cells cannot adequately take up glucose. The body perceives a state of intracellular energy deficit. This triggers two processes:
- Lipolysis: Adipose triglyceride stores are mobilized and oxidized as an alternative fuel source. Progressive loss of fat mass leads to weight loss.
- Gluconeogenesis: Muscle protein is catabolized to provide gluconeogenic amino acids (especially alanine), contributing to loss of lean body mass.
"The inability to move glucose into cells necessitates the oxidation of lipids as an alternative fuel. As a result, adipose stores are used, and a patient with poorly controlled diabetes mellitus loses weight in spite of a good appetite." - Basic Medical Biochemistry: A Clinical Approach, 6e
3. Fatigue
Despite high blood glucose levels, peripheral tissues (muscle, adipose, liver) have reduced glucose uptake due to insulin resistance or insufficient insulin action. Since glucose is the primary fuel for ATP generation, cells are in a relative state of energy starvation. This manifests as persistent fatigue and weakness. Additionally:
- Dehydration from polyuria impairs circulatory efficiency
- Protein catabolism depletes muscle mass, reducing physical capacity
- Chronic hyperglycemia causes non-enzymatic glycation of proteins, impairing tissue function
Together, these mechanisms create the classic symptom profile this patient presents with.
iii) Beneficial Role of Regular Exercise (4 marks)
Exercise is highly beneficial in T2DM through several insulin-independent and insulin-sensitizing mechanisms:
A. Insulin-Independent GLUT4 Translocation (Most Important Mechanism)
During muscle contraction, AMP kinase (AMPK) is activated due to rising AMP:ATP ratio. AMPK triggers the translocation of GLUT4 transporters from intracellular vesicles to the sarcolemma (plasma membrane of muscle cells). This increases glucose uptake into skeletal muscle without requiring insulin.
"Contractile activity triggers the translocation of additional GLUT4 transporters from the cytosol to the plasma membrane. This process, which is insulin independent and is likely mediated by activation of AMP kinase, supports increased glucose uptake. Because exercise-induced translocation of GLUT4 does not depend on insulin, endurance exercise is an important adjunct in controlling elevated levels of blood glucose in patients with diabetes." - Medical Physiology (Boron & Boulpaep)
B. Increased Insulin Sensitivity
"Regular exercise training can also produce prolonged increases in insulin sensitivity." - Ganong's Review of Medical Physiology, 26e
This means that even at rest, the tissues respond better to whatever insulin is available, reducing chronic hyperglycemia.
C. Sustained Post-Exercise Glucose Uptake
The increase in GLUT4 at the muscle membrane persists for several hours after exercise ends, providing prolonged glucose-lowering benefit beyond the exercise session itself.
D. Additional Metabolic Benefits
- Reduces body weight, decreasing insulin resistance (adipose tissue is a major source of inflammatory cytokines that worsen insulin resistance)
- Improves cardiovascular risk profile (reduces BP, LDL, and triglycerides)
- Decreases hepatic glucose output over time
- Increases mitochondrial density in muscle, improving glucose oxidative capacity
Note: In patients on insulin therapy, exercise can precipitate hypoglycemia because both GLUT4 translocation and enhanced insulin absorption occur simultaneously. Such patients should monitor blood glucose and adjust caloric intake or insulin dosage accordingly (Ganong's, 26e).
iv) Hormones Synthesized from the Endocrine Pancreas (3 marks)
The endocrine pancreas consists of the Islets of Langerhans, which contain several distinct cell types, each secreting specific hormones:
| Cell Type | % of Islet Mass | Hormone Secreted |
|---|---|---|
| B (β) cells | ~70% | Insulin (+ C-peptide, amylin) |
| A (α) cells | ~10% | Glucagon |
| D cells | ~5% | Somatostatin |
| F cells (PP cells) | ~15% | Pancreatic Polypeptide (PP) |
| D₂ cells | ~5% | Vasoactive Intestinal Peptide (VIP) |
| EC cells | <1% | Substance P, Serotonin |
Source: Mulholland and Greenfield's Surgery, 7e; Ganong's Review of Medical Physiology, 26e; Guyton & Hall Textbook of Medical Physiology
The four primary hormones enumerated for examination purposes are:
- Insulin - lowers blood glucose; promotes anabolism (glycogen, fat, protein synthesis)
- Glucagon - raises blood glucose; promotes glycogenolysis and gluconeogenesis
- Somatostatin - inhibits secretion of both insulin and glucagon via paracrine action; also inhibits pancreatic polypeptide
- Pancreatic Polypeptide (PP) - inhibits exocrine pancreatic secretion; modulates GI motility
Additionally, amylin (co-secreted with insulin from β cells) slows gastric emptying and suppresses glucagon, and ghrelin is present in small amounts in some islet cells.
Summary Table for Quick Revision:
| Question | Key Point |
|---|---|
| Diagnosis | Type 2 Diabetes Mellitus (FPG 180 mg/dL, PPG 300 mg/dL) |
| Polyuria | Osmotic diuresis due to glucosuria above renal threshold |
| Weight loss | Lipolysis + gluconeogenesis from protein due to intracellular glucose starvation |
| Fatigue | Reduced cellular ATP from impaired glucose uptake; dehydration |
| Exercise benefit | AMPK-mediated insulin-independent GLUT4 translocation + increased insulin sensitivity |
| Pancreatic hormones | Insulin, Glucagon, Somatostatin, Pancreatic Polypeptide (+ VIP, amylin, serotonin) |
45 year old woman presented with buffalo hump, moon face, purple striae over abdomen, weight gain, poor healing of wounds. X-ray showed fracture of vertebrae. Fasting blood sugar level was-160 mg/100 ml of blood. i. What is the most probable endocrine disorder in the woman? ii. Explain the mechanism of development of clinical features in the patient. iii. Describe physiological actions of the hormone responsible for this condition. iv) Name two investigations required for confirmation of clinical diagnosis.1+4+8+2
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Clinical Case Analysis: Cushing's Syndrome
i) Most Probable Endocrine Disorder (1 mark)
Cushing's Syndrome (Hypercortisolism)
The hallmark constellation of buffalo hump, moon facies, purple abdominal striae, central weight gain, poor wound healing, vertebral fractures (osteoporosis), and hyperglycemia (fasting blood sugar 160 mg/100 mL) is classic for chronic glucocorticoid excess - Cushing's syndrome.
"The typical patient is characterised by a facial plethora, a buffalo hump and a moon face in combination with hypertension, diabetes, central obesity and proximal muscle-wasting." - Bailey and Love's Short Practice of Surgery, 28e
ii) Mechanism of Development of Clinical Features (4 marks)
All features are a direct result of chronic excess of cortisol acting on multiple target tissues. Cortisol acts genomically via glucocorticoid response elements (GREs) to alter gene transcription across most body tissues.
| Clinical Feature | Mechanism |
|---|---|
| Moon face | Cortisol promotes lipogenesis and fat redistribution to the face (zygomatic fat pads) and posterior neck |
| Buffalo hump | Cervicodorsal fat deposition due to preferential redistribution of fat from periphery to central/visceral depots |
| Central obesity / weight gain | Cortisol stimulates appetite and shifts fat from limbs to trunk and viscera |
| Purple abdominal striae | Catabolic effect of cortisol on skin collagen - cortisol inhibits fibroblast activity and collagen synthesis, thinning the skin. As the abdomen expands with central fat, the fragile, collagen-depleted skin tears, forming purple striae (purple colour from underlying vascularity) |
| Poor wound healing | Cortisol suppresses the inflammatory response (inhibits phospholipase A₂ and prostaglandin synthesis) and inhibits fibroblast proliferation/collagen deposition, both essential for wound repair. Immune suppression also impairs defence against infection |
| Vertebral fractures (osteoporosis) | Cortisol inhibits osteoblast activity (reduces bone formation), stimulates osteoclast activity (increases bone resorption), and decreases intestinal calcium absorption while increasing renal calcium excretion - all leading to net bone loss and vertebral compression fractures |
| Hyperglycemia (FBS 160 mg/dL) | Cortisol is a counter-regulatory hormone: (a) stimulates hepatic gluconeogenesis, (b) induces insulin resistance in peripheral tissues (muscle and adipose cannot effectively take up glucose), and (c) stimulates proteolysis in muscle to supply gluconeogenic amino acids. This results in steroid-induced diabetes |
| Fatigue / proximal myopathy | Catabolic effect on skeletal muscle protein - cortisol promotes proteolysis to provide gluconeogenic substrates, leading to progressive muscle wasting, especially of proximal limb muscles ("lemon on sticks" appearance with thin arms/legs and central obesity) |
iii) Physiological Actions of Cortisol (8 marks)
Cortisol is synthesised in the zona fasciculata of the adrenal cortex. It is the primary glucocorticoid in humans, secreted under the control of ACTH from the pituitary (which is itself driven by CRH from the hypothalamus), following a diurnal rhythm (peak in early morning). Most body tissues are target sites, as cortisol acts through intracellular glucocorticoid receptors (GRs) that bind to GREs on DNA.
1. Carbohydrate Metabolism (Hyperglycaemic Effect)
- Stimulates hepatic gluconeogenesis (upregulates key enzymes: PEPCK, glucose-6-phosphatase)
- Causes insulin resistance in peripheral tissues - muscle and adipose cannot efficiently take up glucose
- Provides gluconeogenic substrate via protein catabolism (alanine, glutamine from muscle)
- Net effect: raises blood glucose - explains the hyperglycaemia in this patient
2. Protein Metabolism (Catabolic)
- Promotes protein catabolism in muscle, skin, bone, and lymphoid tissue
- Increases circulating amino acids for hepatic gluconeogenesis
- Decreases protein synthesis in most tissues except the liver
- Results in muscle wasting, thin skin, poor wound healing, osteoporosis
3. Fat Metabolism (Lipolytic + Redistribution)
- Stimulates lipolysis in peripheral fat depots (limbs) - mobilises fatty acids for energy
- Promotes lipogenesis and fat deposition in central areas (face, neck, trunk, abdomen)
- Paradoxically, excess cortisol increases appetite and promotes visceral fat accumulation
- Raises plasma free fatty acids - contributes to hyperlipidaemia
4. Anti-inflammatory and Immunosuppressive Actions
- Inhibits phospholipase A₂ (preventing arachidonic acid release) - reduces prostaglandin, thromboxane, and leukotriene synthesis
- Stabilises lysosomal membranes, reducing release of inflammatory mediators
- Inhibits proliferation of T-lymphocytes and reduces lymphocyte and eosinophil counts
- Reduces capillary permeability and oedema at inflammatory sites
- Suppresses macrophage activity and cytokine production (IL-1, IL-6, TNF-α)
- This is the basis of therapeutic glucocorticoid use in autoimmune/inflammatory disease
5. Effects on Bone and Calcium Metabolism
- Inhibits osteoblast-mediated bone formation
- Promotes osteoclastic bone resorption
- Decreases intestinal calcium absorption (antagonises vitamin D action)
- Increases renal calcium excretion
- Net result: osteoporosis and hypercalciuria (risk of renal stones)
6. Cardiovascular Effects
- Maintains vascular responsiveness to catecholamines (permissive effect)
- Has weak mineralocorticoid activity - promotes Na⁺ retention and K⁺ excretion
- Excess cortisol causes hypertension (seen in ~85% of Cushing's patients)
7. CNS Effects
- Affects mood, cognition, and behaviour
- Physiological levels are needed for normal memory and emotional regulation
- Excess causes depression, anxiety, cognitive impairment, or occasionally euphoria/psychosis
8. Stress Response
- Cortisol is the primary stress hormone - levels rise sharply during physical/psychological stress (surgery, trauma, infection)
- Ensures adequate glucose supply to the brain and vital organs during stress
- Has a permissive effect on glucagon and catecholamine actions
9. Effects on Haematopoiesis
- Increases circulating neutrophils (by promoting release from bone marrow and reducing margination)
- Decreases circulating lymphocytes, eosinophils, and monocytes
- Produces the characteristic "stress leucogram" (neutrophilia + lymphopenia)
10. Developmental/Permissive Actions
- Required for normal lung maturation in the foetus (promotes surfactant synthesis)
- Permissive for normal renal tubular function
iv) Investigations for Confirmation (2 marks)
The standard screening tests, two of which must be abnormal to confirm the diagnosis (Endocrine Society guidelines):
1. 24-Hour Urinary Free Cortisol (UFC)
- Measures total cortisol excreted in urine over 24 hours
- In Cushing's syndrome, UFC is markedly elevated (typically >3-4x upper limit of normal)
- Must include concurrent creatinine to verify completeness of collection
- A direct, integrated measure of daily cortisol production
2. Overnight Low-Dose Dexamethasone Suppression Test (1 mg DST)
- 1 mg dexamethasone given orally at 11 PM; plasma cortisol measured at 8 AM next morning
- Normal individuals suppress cortisol to <1.8 μg/dL
- In Cushing's syndrome, cortisol is not suppressed (failure of negative feedback), because the autonomous cortisol source (pituitary adenoma, adrenal tumour, or ectopic ACTH) is resistant to feedback inhibition
- Best initial screening test; sensitivity ~95%
"Overall, 24-hour urinary tests for free cortisol and the overnight dexamethasone suppression test at the 5 μg/dL cutoff have the highest specificity for the diagnosis of Cushing's syndrome." - Schwartz's Principles of Surgery, 11e
Additional tests (for aetiology):
- Plasma ACTH level (distinguishes ACTH-dependent vs. ACTH-independent causes)
- Late-night salivary cortisol (loss of diurnal rhythm)
- High-dose DST (8 mg) and CRH stimulation test (to localise cause)
- MRI pituitary / CT adrenals (imaging, only after biochemical confirmation)
Summary for Revision:
| Question | Key Answer |
|---|---|
| Diagnosis | Cushing's Syndrome (hypercortisolism) |
| Responsible hormone | Cortisol (excess) |
| Site of synthesis | Zona fasciculata of adrenal cortex |
| Buffalo hump / moon face | Central fat redistribution by cortisol |
| Purple striae | Collagen breakdown → skin thinning → tearing |
| Poor wound healing | Anti-inflammatory + anti-fibroblast effect of cortisol |
| Vertebral fractures | Cortisol-induced osteoporosis |
| Hyperglycaemia | Gluconeogenesis + insulin resistance |
| Investigations | 24-hr UFC + Overnight 1 mg DST |
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