Practice 9 structured short- and long-answer medical questions on Endocrine & Renal Pathology — Must Know Notes. Review model answers for exam revision.
Answer: ## Summary This document provides concise, essential notes on endocrine and renal pathology, covering key diseases, their causes, clinical presentations, diagnostic methods, and treatment approaches. It emphasizes critical differences between related conditions, such as primary versus secondary adrenal insufficiency, and outlines the pathophysiology and management of diabetes mellitus, parathyroid disorders, and renal pathologies like acute kidney injury and chronic kidney disease. The notes also touch upon lung tumours and lung transplantation, highlighting their crucial aspects for medical understanding. ## Key Points - ## Summary This document provides concise, essential notes on endocrine and renal pathology, covering key diseases, their causes, clinical presentations, diagnostic methods, and treatment approaches. - It emphasizes critical differences between related conditions, such as primary versus secondary adrenal insufficiency, and outlines the pathophysiology and management of diabetes mellitus, parathyroid disorders, and renal pathologies like acute kidney injury and chronic kidney disease. - The notes also touch upon lung tumours and lung transplantation, highlighting their crucial aspects for medical understanding. - ## Key Points - **Adrenal Insufficiency (Addison's Disease):** Inadequate cortisol ± aldosterone production due to primary (autoimmune, TB) or secondary (steroid use, pituitary issues) causes. - Primary leads to hyperpigmentation and electrolyte imbalances due to ↑ACTH, while secondary does not cause hyperpigmentation and has intact aldosterone. - - **Cushing's Syndrome:** Chronic excess cortisol from exogenous steroids (most common) or endogenous causes like pituitary ACTH adenoma (Cushing's disease), ectopic ACTH, or adrenal tumours. - Presents with characteristic central obesity, moon face, and metabolic disturbances. - - **Hyperaldosteronism (Conn's Syndrome):** Excess aldosterone leading to hypertension and hypokalaemia. ## Detailed Notes ## Key Points - **Adrenal Insufficiency (Addison's Disease):** Inadequate cortisol ± aldosterone production due to primary (autoimmune, TB) or secondary (steroid use, pituitary issues) causes. Primary leads to hyperpigmentation and electrolyte imbalances due to ↑ACTH, while secondary does not cause hyperpigmentation and has intact aldosterone. - **Cushing's Syndrome:** Chronic excess cortisol from exogenous steroids (most common) or endogenous causes like pituitary ACTH adenoma (Cushing's disease), ectopic ACTH, or adrenal tumours. Presents with characteristic central obesity, moon face, and metabolic disturbances. - **Hyperaldosteronism (Conn's Syndrome):** Excess aldosterone leading to hypertension and hypokalaemia. Primary (adenoma/hyperplasia) shows suppressed renin, while secondary has elevated renin. - **Phaeochromocytoma:** Catecholamine-secreting tumour of the adrenal medulla, causing paroxysmal hypertension, palpitations, and sweating. - **Diabetes Mellitus:** Type 1 (autoimmune β-cell destruction, absolute insulin deficiency) and Type 2 (insulin resistance, relative deficiency). Diagnosis via glucose levels or HbA1c. DKA (Type 1) and HHS (Type 2) are acute complications. - **Parathyroid Disorders:** Primary hyperparathyroidism (autonomous PTH overproduction) causes ↑Ca²⁺, ↓phosphate. Secondary (renal failure) causes compensatory ↑PTH. Hypoparathyroidism leads to ↓Ca²⁺, ↑phosphate. - **Porphyrias:** Enzyme defects in haem biosynthesis. Acute porphyrias are neurovisceral, while cutaneous porphyrias cause photosensitivity. Triggers are crucial. - **Renal Function Evaluation:** GFR is the best marker. BUN:Creatinine ratio, FENa, and urine casts are vital for diagnosing AKI and understanding intrinsic renal disease. - **Acute Kidney Injury (AKI):** Rapid decline in renal function (creatinine rise, ↓ urine output). Classified as prerenal (↓ perfusion), intrinsic (ATN, AIN, GN), or postrenal (obstruction). - **Chronic Kidney Disease (CK D):** Progressive loss of renal function (eGFR <60). Causes include diabetes and hypertension. Complications include anaemia, secondary hyperparathyroidism, and cardiovascular disease. - **Renal Calculi:** Stones formed in the urinary tract. Types include calcium oxalate, uric acid, struvite, and cystine. Clinical features include colic and haematuria. - **Lung Tumours:** Primarily carcinomas (adenocarcinoma, squamous cell, small cell, large cell). Smoking is the main risk factor. Small cell lung cancer is aggressive and metastatic at diagnosis. - **Lung Transplantation:** For end-stage lung disease. Complications include infections, acute rejection, and chronic rejection (bronchiolitis obliterans). ## Detailed Notes ### 1. ADRENAL INSUFFICIENCY (ADDISON'S DISEASE) **Definition:** Inadequate cortisol ± aldosterone production. **Primary causes:** Autoimmune (most common in developed world), TB (most common in developing world), Waterhouse-Friderichsen syndrome (meningococcal sepsis leading to bilateral adrenal haemorrhage), metastases, fungal infections. **Secondary causes:** Prolonged steroid use (most common overall), pituitary tumours, Sheehan's syndrome. **Key difference:** - **Primary:** ↑ACTH → hyperpigmentation, hyponatraemia, hyperkalaemia. - **Secondary:** ↓ACTH → NO hyperpigmentation, aldosterone intact. **Clinical features:** Fatigue, weight loss, postural hypotension, salt craving, nausea, hypoglycaemia. Hyperpigmentation is present in primary adrenal insufficiency. **Diagnosis:** Short ACTH stimulation test (cortisol fails to rise is the gold standard). Also: ↑ACTH (primary), ↓ACTH (secondary), hyponatraemia, hyperkalaemia, hypoglycaemia, anti-21-hydroxylase antibodies. **Morphology:** - Autoimmune: Small, atrophic glands with lymphocytic infiltration. - TB: Enlarged glands with caseating granulomas. - Waterhouse-Friderichsen: Bilateral haemorrhagic necrosis. **Treatment:** Hydrocortisone + fludrocortisone (for primary). Stress doses are required during illness or surgery. ### 2. CUSHING'S SYNDROME **Definition:** Chronic excess of cortisol, either exogenous or endogenous. **Causes:** - **Exogenous steroids:** Most common overall cause. Leads to bilateral adrenal atrophy. - **Cushing's Disease:** Pituitary ACTH adenoma (70% of endogenous cases). Leads to bilateral adrenal hyperplasia. - **Ectopic ACTH:** From tumours like small cell lung cancer or carcinoid tumours. Rapid onset, hyperpigmentation, severe hypokalaemia. - **Adrenal adenoma/carcinoma:** ACTH-independent. **Clinical features:** Central obesity, moon face, buffalo hump, purple striae, proximal muscle weakness, hypertension, hyperglycaemia, osteoporosis, hirsutism, amenorrhoea, depression. **Diagnosis:** - **Confirmation:** 24-hour urinary free cortisol, 1mg overnight dexamethasone suppression test (cortisol not suppressed). - **Find cause:** Plasma ACTH level (↑ suggests ACTH-dependent; ↓ suggests adrenal cause). - **Localisation:** Pituitary MRI, CT scan of the adrenals, high-dose dexamethasone suppression test. **Morphology:** - Pituitary adenoma: Small, basophilic corticotroph adenoma, ACTH positive on immunohistochemistry. - Adrenal adenoma: Yellow, well-circumscribed tumour composed of uniform clear cells. - Adrenal carcinoma: Large, necrotic, pleomorphic, and invasive tumour. **Treatment:** Surgery (transsphenoidal for pituitary adenoma, adrenalectomy for adrenal tumours). Medical management includes ketoconazole, metyrapone, or mifepristone. ### 3. HYPERALDOSTERONISM (CONN'S SYNDROME) **Definition:** Excess aldosterone production, leading to hypertension and hypokalaemia. **Primary (Conn's):** Caused by adrenal adenoma (70%) or bilateral adrenal hyperplasia. Aldosterone production is autonomous, leading to **suppressed renin**. **Secondary:** Occurs in states of high renin (e.g., renal artery stenosis, heart failure, cirrhosis). **Renin is elevated**. **Clinical features:** Hypertension (often resistant to treatment), hypokalaemia (causing weakness, cramps, polyuria), metabolic alkalosis. Edema is typically absent. **Diagnosis:** Elevated aldosterone level combined with a suppressed renin level, and an **elevated aldosterone:renin ratio (>30)** strongly suggests primary hyperaldosteronism. CT scan of the adrenals is performed. Adrenal venous sampling may be needed to confirm lateralisation of the lesion. **Treatment:** Adrenalectomy for adenoma. Spironolactone for bilateral hyperplasia. ### 4. PHAEOCHROMOCYTOMA **Definition:** A catecholamine-secreting tumour of the adrenal medulla chromaffin cells. **Rule of 10s:** 10% bilateral, 10% malignant, 10% extra-adrenal, 10% familial (associated with MEN2, VHL, NF1). **Clinical features (The 5 Ps):** Palpitations, Perspiration, Pallor, Pain (headache), Pressure (hypertension, often paroxysmal). **Diagnosis:** 24-hour urinary catecholamines and metanephrines (gold standard). Plasma metanephrines are a sensitive screening test. CT or MRI of the adrenals. MIBG scan can confirm functional tissue and detect extra-adrenal lesions. **Treatment:** Alpha-blockade FIRST (e.g., phenoxybenzamine), followed by beta-blockade, and then surgery. Beta-blockers should never be administered first. ### 5. DIABETES MELLITUS **Type 1:** Autoimmune destruction of pancreatic β-cells, leading to absolute insulin deficiency. Typically affects young, thin individuals and is prone to Diabetic Ketoacidosis (DKA). Associated with anti-GAD and anti-islet antibodies, and HLA-DR3/DR4. **Type 2:** Characterised by insulin resistance and a relative deficiency in insulin secretion. Usually affects older, obese individuals with an insidious onset. Ketoacidosis is uncommon. Strong family history is common. **Diagnosis:** - Fasting plasma glucose ≥7.0 mmol/L - Random plasma glucose ≥11.1 mmol/L - HbA1c ≥48 mmol/mol (6.5%) - Oral Glucose Tolerance Test (OGTT) 2-hour plasma glucose ≥11.1 mmol/L **DKA (Type 1):** Caused by severe insulin deficiency leading to hyperglycaemia, lipolysis, ketone production, and metabolic acidosis. Common triggers include infection and missed insulin doses. Features include Kussmaul breathing, acetone breath, dehydration, elevated glucose, low pH, low bicarbonate, and elevated potassium (total body potassium is depleted and requires replacement once insulin therapy begins). Management involves IV fluids, insulin infusion, and potassium replacement. **HHS (Type 2):** Characterised by very high glucose levels (>30 mmol/L), markedly elevated serum osmolality, absence of significant ketosis, and no significant acidosis. It has a high mortality rate. Management prioritises fluid resuscitation, followed cautiously by insulin. **Chronic complications:** - **Microvascular:** Nephropathy (Kimmelstiel-Wilson nodules), retinopathy, neuropathy. - **Macrovascular:** Ischaemic heart disease (leading cause of death), stroke, peripheral arterial disease. ### 6. PARATHYROID DISORDERS **PTH actions:** Increases renal calcium reabsorption, increases phosphate excretion, increases vitamin D activation in the kidney, leading to increased intestinal calcium absorption and increased osteoclastic bone resorption. The net effect is an increase in serum calcium. ### Primary Hyperparathyroidism Caused by autonomous overproduction of PTH. Most commonly due to an adenoma (85–95%), followed by hyperplasia (5–10%). Carcinoma is rare (1%). It is more common in women. **Clinical features:** Often referred to as "painful bones, renal stones, abdominal groans, psychic moans." However, most patients are asymptomatic and it is found incidentally on routine biochemistry. **Biochemistry:** Elevated serum calcium, inappropriately elevated or normal PTH, low serum phosphate, and elevated urinary calcium. **Morphology:** Adenoma is typically a solitary, yellow, well-circumscribed lesion composed of chief cells, with a rim of normal parathyroid tissue. Carcinoma is grey-white, invasive, and diagnosis requires evidence of invasion into surrounding structures or metastasis. **Treatment:** Parathyroidectomy is the definitive treatment. Medical options include cinacalcet and bisphosphonates. ### Secondary Hyperparathyroidism A compensatory increase in PTH in response to chronic hypocalcaemia. The most common cause is chronic renal failure. All four parathyroid glands are typically hyperplastic. Biochemistry shows low calcium, elevated PTH, and elevated phosphate. Treatment involves vitamin D supplementation and phosphate binders. ### Tertiary Hyperparathyroidism Develops after prolonged secondary hyperparathyroidism, where the parathyroid glands become autonomous in PTH secretion, even after successful renal transplantation. This results in elevated calcium and elevated PTH. Parathyroidectomy is often required. ### Hypoparathyroidism Results from a deficiency in PTH, leading to hypocalcaemia and hyperphosphataemia. **Causes:** Post-surgical (most common acquired cause), autoimmune (in Autoimmune Polyendocrine Syndrome-1, APS-1, due to AIRE gene mutation), DiGeorge syndrome (22q11 deletion), and hypomagnesaemia. **Clinical features:** Tetany, characterised by circumoral tingling, carpopedal spasm, laryngospasm, and seizures. Positive Chvostek's and Trousseau's signs. Can lead to prolonged QT interval on ECG, cataracts, basal ganglia calcification, and dental abnormalities. **Treatment:** Acute hypocalcaemia is treated with intravenous calcium gluconate. Chronic management involves oral calcium supplements and calcitriol. ### Pseudohypoparathyroidism A group of genetic disorders caused by resistance to PTH, often due to mutations in the Gsα subunit of the G-protein coupled receptor. Characterised by elevated PTH levels, low serum calcium, and elevated phosphate. Patients may exhibit Albright's hereditary osteodystrophy, a condition with short stature, short fourth metacarpal, obesity, and a round face. ### 7. PORPHYRIAS **Definition:** A group of genetic disorders caused by enzyme defects in the haem biosynthesis pathway, leading to the accumulation of porphyrins or their precursors (such as ALA and PBG). **Acute porphyrias:** Characterised by neurovisceral symptoms, including severe abdominal pain, motor neuropathy, autonomic dysfunction (tachycardia, hypertension), and psychiatric symptoms. Urine may darken upon standing. The key diagnostic test during an attack is **urinary porphobilinogen (PBG)**, which will be elevated. **Cutaneous porphyrias:** Manifest with photosensitivity, leading to blistering, burning sensations, hyperpigmentation, and scarring of sun-exposed skin. Diagnosis is made by measuring **plasma porphyrins**. **Triggers:** Various factors can precipitate attacks or worsen symptoms, including barbiturates, sulfonamides, anti-epileptic drugs, alcohol, oestrogens, fasting, stress, and infections. **Management:** The cornerstone of management is avoiding known triggers. For acute attacks, treatment includes intravenous haem arginate and high carbohydrate loading. For cutaneous porphyrias, sun avoidance is crucial. Phlebotomy may be used for porphyria cutanea tarda (PCT). ### 8. RENAL FUNCTION EVALUATION **Glomerular Filtration Rate (GFR):** The best overall indicator of kidney function. Estimated GFR (eGFR) is commonly calculated using the CKD-EPI formula. Cystatin C is an alternative marker that is less affected by muscle mass. **BUN:Creatinine Ratio:** - **>20:1:** Suggests prerenal azotaemia (reduced kidney perfusion). - **~10:1:** Suggests intrinsic renal disease. **Proteinuria:** - Normal: <30 mg/day. - Microalbuminuria: 30–300 mg/day. - Macroalbuminuria: >300 mg/day. - Nephrotic range proteinuria: >3.5 g/day. **FENa (Fractional Excretion of Sodium):** - **<1%:** Suggests prerenal azotaemia. - **>2%:** Suggests intrinsic renal disease, particularly Acute Tubular Necrosis (ATN). **Must-know urine casts:** - **RBC casts:** Indicate glomerulonephritis. - **WBC casts:** Suggest pyelonephritis or acute interstitial nephritis (AIN). - **Muddy brown granular casts:** Characteristic of ATN. - **Fatty casts:** Associated with nephrotic syndrome. - **Broad waxy casts:** Indicate chronic kidney disease (CKD). ### 9. ACUTE KIDNEY INJURY (AKI) **Definition:** A rapid decline in kidney function, defined by any of the following criteria within 48 hours: - Increase in serum creatinine by ≥26.5 μmol/L. - Increase in serum creatinine to ≥1.5 times baseline. - Urine output <0.5 mL/kg/hr for more than 6 hours. **Prerenal AKI:** Caused by decreased renal perfusion. Common causes include hypovolaemia, heart failure, sepsis, NSAIDs, and ACE inhibitors. Characterised by FENa <1%, urine sodium <20 mEq/L, specific gravity >1.020, and hyaline casts. It typically responds to fluid resuscitation. **Intrinsic AKI:** Damage to the kidney parenchyma. - **ATN (Acute Tubular Necrosis):** The most common cause of intrinsic AKI. Can be ischaemic or nephrotoxic (e.g., from aminoglycosides, contrast dye, myoglobin). Characterised by FENa >2% and muddy brown granular casts. - **AIN (Acute Interstitial Nephritis):** Often a drug hypersensitivity reaction (e.g., NSAIDs, penicillins). Presents with WBC casts and eosinophils in urine. The classic triad includes fever, rash, and eosinophilia, but not all features are always present. - **Glomerulonephritis:** Immune-mediated inflammation of the glomeruli. Characterised by RBC casts and proteinuria. **Postrenal AKI:** Caused by obstruction of the urinary tract. Common causes include benign prostatic hyperplasia (BPH), kidney stones, and malignancy. Hydronephrosis may be seen on ultrasound. **Complications of AKI:** Hyperkalaemia (the most dangerous), metabolic acidosis, fluid overload, and uraemia. ### 10. CHRONIC KIDNEY DISEASE (CKD) **Definition:** Kidney damage or an eGFR <60 mL/min/1.73m² for ≥3 months. **Causes:** - Diabetic nephropathy (most common). - Hypertensive nephropathy (second most common). - Chronic glomerulonephritis. - Polycystic kidney disease (PKD). - Obstructive uropathy. **Pathophysiology:** Loss of nephrons leads to compensatory hyperfiltration in the remaining nephrons. This increased workload eventually leads to glomerulosclerosis and further nephron loss, creating a vicious cycle. **Complications:** - **Anaemia:** Due to decreased erythropoietin (EPO) production. - **Secondary hyperparathyroidism:** Due to decreased vitamin D activation and hypocalcaemia, leading to increased PTH. This can cause renal osteodystrophy. - **Electrolyte imbalances:** Hyperkalaemia, metabolic acidosis, hyperphosphataemia. - **Cardiovascular disease:** Hypertension, left ventricular hypertrophy (LVH), and accelerated atherosclerosis. - **Uraemia:** Symptoms include nausea, pruritus, pericarditis, and encephalopathy. **Ultrasound findings:** Typically show small, shrunken kidneys (<9cm), except in conditions like diabetes mellitus and PKD, where kidneys may be normal or enlarged. **Treatment:** Management of underlying causes (e.g., BP control with ACE inhibitors/ARBs, glucose control). Phosphate binders, EPO for anaemia, and dialysis or kidney transplantation for end-stage renal disease (ESRD). ### 11. RENAL CALCULI **Types of stones:** - **Calcium oxalate:** Most common type (70–80%). - **Uric acid:** Radiolucent stones that form in acidic urine. - **Struvite:** Form in alkaline urine, often associated with urinary tract infections (UTIs) caused by urease-producing bacteria. Can form large staghorn calculi. Characterised by "coffin-lid" shaped crystals. - **Cystine:** Form in cystinuria, a genetic disorder of amino acid transport, resulting in hexagonal crystals. **Clinical features:** Loin-to-groin colicky pain, haematuria (microscopic or gross), nausea, and vomiting. Fever in the presence of a kidney stone indicates an infected stone, which is an emergency. **Imaging:** - **Non-contrast CT KUB (Kidneys, Ureters, Bladder):** Gold standard for diagnosis, as it visualises all stone types. - **Ultrasound:** Useful in pregnant women and children, and for evaluating hydronephrosis. - **X-ray KUB:** Only visualises radiopaque stones (calcium oxalate, struvite, cystine). **Management:** - **Conservative:** NSAIDs for pain control, tamsulosin to aid stone passage (for stones <10mm). - **Interventional:** Ureteroscopy, Extracorporeal Shock Wave Lithotripsy (ESWL), Percutaneous Nephrolithotomy (PCNL) for staghorn calculi. - **Prevention:** High fluid intake, treating underlying causes (e.g., metabolic abnormalities). ### 12. LUNG TUMOURS Lung cancers account for 90–95% of lung tumours. Lung cancer is the leading cause of cancer death worldwide. **Risk factors:** Smoking (80% of cases), asbestos exposure, radiation, radon gas, industrial carcinogens. ### Types of Lung Cancer **Adenocarcinoma (50%):** The most common type overall. It is also the most common lung cancer in non-smokers and women. Typically arises peripherally. It is TTF-1 positive. Often driven by mutations in EGFR or ALK, making them targetable with tyrosine kinase inhibitors (TKIs). Precursor lesions include atypical adenomatous hyperplasia (AAH), adenocarcinoma in situ (AIS), microinvasive adenocarcinoma, and invasive adenocarcinoma. **Squamous Cell Carcinoma (20%):** Often located centrally or in the hilum. Strongly associated with smoking. Histologically characterised by keratinisation, squamous pearls, and intercellular bridges. Frequently associated with TP53 mutations. Precursor lesions include metaplasia, dysplasia, and carcinoma in situ (CIS). Can cavitate. May secrete parathyroid hormone-related peptide (PTHrP), leading to hypercalcaemia. **Small Cell Carcinoma (15%):** Almost exclusively associated with smoking. It is the most aggressive type, virtually always metastatic at diagnosis. Treatment is typically chemotherapy, not surgery. Histologically, it shows small cells with scant cytoplasm, salt-and-pepper chromatin, nuclear moulding, and the Azzopardi effect. Universal mutations in TP53 and RB genes. Frequently associated with paraneoplastic syndromes, including SIADH, ectopic ACTH production, and Lambert-Eaton myasthenic syndrome. **Large Cell Carcinoma (2%):** A diagnosis of exclusion, meaning it lacks features of squamous cell carcinoma, adenocarcinoma, or small cell carcinoma. ### Clinical Features of Lung Cancer Common symptoms include cough (75%), weight loss (40%), chest pain (40%), dyspnoea (20%), and haemoptysis. Local effects can include Superior Vena Cava (SVC) obstruction, Pancoast tumour (leading to Horner's syndrome and brachial plexus involvement), hoarseness (due to recurrent laryngeal nerve involvement), and dysphagia. ### Metastatic Tumours to the Lung The lung is the most common site for metastases from other primary cancers. These metastases often appear as "cannonball lesions" – multiple, round nodules scattered throughout the lungs. Common primary cancers that metastasise to the lung include breast, colon, kidney, melanoma, and sarcoma. ### 13. LUNG TRANSPLANTATION **Indications:** End-stage conditions such as Chronic Obstructive Pulmonary Disease (COPD), Idiopathic Pulmonary Fibrosis (IPF), Cystic Fibrosis, and Pulmonary Arterial Hypertension. **Complications:** **Infections:** - **Early (within first 3 months):** Bacterial infections are most common. - **Later (3–12 months):** Cytomegalovirus (CMV), fungal infections (Aspergillus, Candida), and Pneumocystis jirovecii pneumonia (PJP) are more prevalent. **Acute Rejection:** Typically occurs within weeks to months post-transplant. Symptoms can include fever, dyspnoea, and infiltrates on chest imaging, which can mimic infection. Histologically, it is characterised by lymphocytic infiltrates around bronchioles and blood vessels. Acute rejection is usually responsive to treatment. Diagnosis is made via transbronchial biopsy. **Chronic Rejection:** Occurs in ≥50% of patients by 3–5 years post-transplant. The hallmark of chronic rejection is **bronchiolitis obliterans**, a fibrotic process that leads to the occlusion of small airways. This complication is irreversible and cannot be cured. The median survival post-lung transplant is approximately 6 years, largely influenced by the development of chronic rejection. ## Practice Questions
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