3.3 Diabetes Mellitus, Thyroid Disorders & Adrenal Axis Pathologies
Key Takeaways
- Metformin is the first-line pharmacotherapy for Type 2 Diabetes Mellitus; it acts primarily by decreasing hepatic gluconeogenesis and does not cause hypoglycemia.
- Diabetic Ketoacidosis (DKA) requires aggressive IV fluid resuscitation (normal saline initially) followed by continuous IV insulin infusion; monitor and replete potassium carefully.
- Primary hypothyroidism is characterized by an elevated TSH and low free T4; Hashimoto's thyroiditis (anti-TPO antibodies) is the most common cause.
- Graves' disease, the most common cause of hyperthyroidism, presents with suppressed TSH, elevated free T4, and specific signs like exophthalmos and pretibial myxedema.
- Addison's disease (primary adrenal insufficiency) presents with fatigue, hyperpigmentation, hypotension, hyponatremia, and hyperkalemia due to loss of both glucocorticoids and mineralocorticoids.
Diabetes Mellitus, Thyroid Disorders & Adrenal Axis Pathologies
Endocrinology constitutes a core high-yield domain on the SMLE, driven by the exceptional prevalence of Type 2 Diabetes Mellitus (~24% of the adult population) and metabolic syndrome in Saudi Arabia. Master diagnostic criteria, acute emergency resuscitation algorithms, thyroid functional panels, and adrenal diagnostic pathways.
Diabetes Mellitus (DM): Diagnostic Criteria & Pharmacotherapy
Diagnostic Thresholds (ADA & Saudi MOH Guidelines)
Diagnosis requires one of the following four criteria (confirmed by repeat testing on a separate day unless unequivocal hyperglycemia with acute metabolic decompensation is present):
- Fasting Plasma Glucose (FPG): ≥126 mg/dL (7.0 mmol/L) after no caloric intake for at least 8 hours.
- 2-Hour Postprandial Glucose: ≥200 mg/dL (11.1 mmol/L) during an Oral Glucose Tolerance Test (OGTT using 75g anhydrous glucose).
- Glycated Hemoglobin (HbA1c): ≥6.5% (48 mmol/mol).
- Random Plasma Glucose: ≥200 mg/dL in a patient presenting with classic symptoms of hyperglycemia (polyuria, polydipsia, unexplained weight loss, blurred vision).
Pharmacotherapy for Type 2 Diabetes Mellitus
- First-Line Therapy: Metformin (Biguanide). Decreases hepatic gluconeogenesis and increases peripheral insulin sensitivity. Weight-neutral, does not cause hypoglycemia as monotherapy. Major side effect: GI distress. Rare serious risk: Lactic acidosis. Contraindicated if eGFR <30 mL/min/1.73m².
- Second-Line / Add-On Agents:
- SGLT2 Inhibitors (Empagliflozin, Dapagliflozin): Block renal glucose reabsorption in proximal tubule. Proven reduction in CV mortality and heart failure hospitalizations; slows CKD progression. Side effects: Mycotic genital infections, euglycemic DKA.
- GLP-1 Receptor Agonists (Liraglutide, Semaglutide): Enhance glucose-dependent insulin secretion, slow gastric emptying, promote significant weight loss. Proven CV benefit. Side effects: Nausea, pancreatitis risk. Contraindicated in Medullary Thyroid Carcinoma / MEN 2.
- DPP-4 Inhibitors (Sitagliptin): Weight-neutral, low hypoglycemia risk. Do not combine with GLP-1 RAs.
- Sulfonylureas (Gliclazide, Glimepiride): Stimulate pancreatic beta-cell insulin secretion. High risk of hypoglycemia and weight gain.
Acute Diabetic Emergencies: DKA vs. HHS
| Diagnostic Parameter | Diabetic Ketoacidosis (DKA) | Hyperosmolar Hyperglycemic State (HHS) |
|---|---|---|
| Primary Patient Population | Typically Type 1 DM (Absolute insulin deficiency). | Typically Type 2 DM (Relative insulin deficiency; elderly). |
| Serum Glucose | > 250 mg/dL (13.9 mmol/L). | > 600 mg/dL (33.3 mmol/L). |
| Arterial / Venous pH | < 7.30 (Severe metabolic acidosis). | > 7.30 (Normal or mild acidosis). |
| Serum Bicarbonate | < 18 mEq/L | > 18 mEq/L |
| Anion Gap | High Anion Gap (> 12 mEq/L). | Normal or mildly elevated. |
| Serum / Urine Ketones | Strongly Positive (Beta-hydroxybutyrate). | Absent or trace. |
| Effective Serum Osmolality | Variable | > 320 mOsm/kg (Severe hyperosmolality). |
| Dominant Clinical Signs | Kussmaul breathing (deep, rapid respiration), fruity acetone breath, diffuse abdominal pain, nausea/vomiting. | Profound dehydration, stupor, coma, focal neurological deficits. |
Unified DKA/HHS Management Algorithm:
- IV Fluid Resuscitation (Priority #1): Administer 1.0–1.5 L of 0.9% Normal Saline over the first hour to restore intravascular volume.
- Insulin Therapy: Continuous IV regular insulin infusion (0.1 units/kg/hr). When glucose falls to ~200 mg/dL in DKA (or ~300 in HHS), add 5-10% Dextrose to IV fluids to prevent hypoglycemia while continuing insulin to clear ketoacidosis.
- Potassium Management (CRITICAL): Total body potassium is depleted due to osmotic diuresis. Insulin drives potassium into cells:
- If K+ <3.3 mEq/L: HOLD INSULIN; give IV KCl until K+ >3.3 mEq/L.
- If K+ 3.3–5.2 mEq/L: Add 20-30 mEq KCl per liter of IV fluid to maintain K+ between 4.0 and 5.0 mEq/L.
- If K+ >5.2 mEq/L: Do not add K+ to fluids; recheck K+ every 2 hours.
Thyroid Axis Dysfunction
Primary Hypothyroidism
- Labs: High TSH, Low Free T4. (Subclinical: High TSH, Normal Free T4).
- Etiology: Hashimoto's Thyroiditis (chronic lymphocytic thyroiditis) is the most common cause. Marked by anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin antibodies. Histology: Lymphocytic infiltrate with germinal centers and Hürthle cells.
- Presentation: Fatigue, cold intolerance, weight gain, constipation, dry skin, non-pitting periorbital edema, delayed relaxation of deep tendon reflexes.
- Treatment: Levothyroxine (synthetic T4). Take on an empty stomach 30-60 mins before breakfast. Monitor TSH at 6-8 weeks to adjust dosing.
Hyperthyroidism & Thyrotoxicosis
- Labs: Low / Suppressed TSH (<0.01), High Free T4 / T3.
- Graves' Disease: Most common cause. Caused by Thyroid-Stimulating Immunoglobulins (TSI) binding TSH receptors. Triad: (1) Thyrotoxicosis; (2) Exophthalmos (Proptosis) due to retro-orbital fibroblast glycosaminoglycan accumulation; (3) Pretibial Myxedema (infiltrative dermopathy).
- Pharmacotherapy:
- Symptom control: Beta-blockers (Propranolol blocks peripheral T4 to T3 conversion).
- Antithyroid Drugs (Thionamides): Methimazole (first-line in non-pregnant patients; teratogenic in 1st trimester causing aplasia cutis). Propylthiouracil (PTU) (first-line in 1st trimester of pregnancy and in Thyroid Storm because it inhibits peripheral T4 to T3 conversion). Major rare side effect of both: Agranulocytosis (fever + sore throat mandates immediate CBC).
- Thyroid Storm Management: Beta-blockers + PTU + IV Potassium Iodide (Lugol's solution, given 1 hour AFTER PTU to block organification via Wolff-Chaikoff effect) + IV Hydrocortisone.
Adrenal Axis Pathologies
- Adrenal Insufficiency (Addison's Disease - Primary): Autoimmune destruction of adrenal cortex. Loss of cortisol and aldosterone. Clinical features: Hypotension, hyponatremia, hyperkalemia, fatigue, and hyperpigmentation (elevated ACTH stimulates melanocytes via MSH co-secretion). Diagnosis: 8 AM Cortisol (low) followed by Cosyntropin (synthetic ACTH) Stimulation Test (failure of cortisol to double confirms primary AI). Treatment: Hydrocortisone + Fludrocortisone.
- Cushing's Syndrome (Hypercortisolism): Features: Moon facies, buffalo hump, abdominal striae, hypertension, hyperglycemia, proximal muscle weakness. Diagnostic Workup: Screening via 24h Urine Free Cortisol or Overnight 1mg Dexamethasone Suppression Test (failure to suppress cortisol <1.8 mcg/dL confirms hypercortisolism). Next step: Plasma ACTH (Low = Adrenal adenoma; High = ACTH-dependent: Pituitary adenoma vs. Ectopic SCLC).
- Pheochromocytoma: Catecholamine-secreting tumor of adrenal medulla chromaffin cells. Triad: Episodic Headaches, Sweating, Tachycardia + Severe Hypertension. Diagnosis: Plasma free metanephrines or 24h urinary fractionated metanephrines. Management: Alpha-blocker FIRST (Phenoxybenzamine) for 10-14 days before surgery; then add Beta-blocker. (Never give Beta-blocker first; causes unopposed alpha-1 stimulation leading to hypertensive crisis!).
Osteoporosis
Osteoporosis is a skeletal disorder of low bone mass and microarchitectural deterioration that increases fracture risk; the SMLE tests screening and first-line therapy in postmenopausal women and chronic-steroid users.
- Screening: DEXA scan at age ≥65 for women and ≥70 for men, or earlier with risk factors (chronic glucocorticoid use, early menopause, low body weight, smoking, family history of hip fracture). A T-score ≤ −2.5 defines osteoporosis; −1.0 to −2.5 is osteopenia.
- Treatment: First-line is a bisphosphonate (alendronate); ensure adequate calcium (1,000–1,200 mg/day) and vitamin D (800–1,000 IU/day). For glucocorticoid-induced osteoporosis, start bisphosphonate prophylaxis concurrently with chronic steroids.
- Saudi relevance: Despite a sunny climate, vitamin D deficiency is highly prevalent in Saudi Arabia, driven by limited skin sun exposure and an indoor lifestyle; a low serum 25-OH-D is a modifiable risk factor emphasized on the exam.
A 32-year-old woman presents to the clinic complaining of feeling constantly "on edge," excessive sweating, and a 6-kg weight loss over the past 3 months despite an increased appetite. She also notes that her eyes feel gritty and look "bulging." On physical examination, her heart rate is 115 bpm and regular. Her skin is warm and moist. She has a fine tremor in her outstretched hands and noticeable bilateral proptosis. Laboratory testing shows a TSH of <0.01 μIU/mL (normal 0.4-4.0) and an elevated free T4. Which of the following autoantibodies is most specific for the underlying cause of this patient's condition?
A 19-year-old male with a known history of type 1 diabetes mellitus is brought to the emergency department by his roommate. He has been complaining of abdominal pain and vomiting for the past 24 hours. The roommate mentions he has been out of his insulin for three days. On examination, he is lethargic with deep, rapid, sighing respirations. His breath has a distinct fruity odor. Capillary blood glucose is "HIGH" on the glucometer. Stat laboratory results reveal a serum glucose of 550 mg/dL, pH of 7.15, bicarbonate of 12 mEq/L, and a serum potassium of 4.8 mEq/L. He is diagnosed with Diabetic Ketoacidosis (DKA). After initiating aggressive intravenous fluid resuscitation with normal saline, what is the most appropriate next step regarding his insulin and electrolyte management?
A 45-year-old man presents to the clinic with complaints of profound weakness, fatigue, and a 10 kg weight loss over the past 6 months. He reports craving salty foods and feeling lightheaded when standing up. Physical examination reveals a blood pressure of 90/60 mmHg sitting, which drops to 75/50 mmHg upon standing. He has increased pigmentation over his palmar creases and oral mucosa. Laboratory studies show a serum sodium of 130 mEq/L (normal 135-145) and serum potassium of 5.6 mEq/L (normal 3.5-5.0). A morning serum cortisol level is appropriately checked and found to be remarkably low. What is the most definitive diagnostic test to confirm the primary etiology of this patient's condition?