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"diabetes mellitus"[MeSH Terms] AND management

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Diabetes Mellitus - Complete Overview

Definition

Diabetes mellitus (DM) is a group of metabolic disorders characterized by chronic hyperglycemia resulting from defects in insulin secretion, insulin action, or both. The resulting hyperglycemia leads to long-term damage, dysfunction, and failure of multiple organ systems.

Classification (ADA)

The ADA recognizes four major clinical types:
  1. Type 1 DM (T1DM) - Autoimmune beta-cell destruction leading to absolute insulin deficiency. Accounts for 5-10% of all DM cases.
  2. Type 2 DM (T2DM) - Progressive loss of beta-cell insulin secretion, frequently on the background of insulin resistance. Most common type (~90%).
  3. Gestational DM (GDM) - Diabetes diagnosed in pregnancy that was not clearly overt prior to gestation.
  4. Other specific types - Monogenic diabetes (MODY, neonatal), exocrine pancreatic disease (cystic fibrosis, pancreatitis), drug-induced (glucocorticoids, HIV treatment, post-transplant).
(Creasy & Resnik's Maternal-Fetal Medicine, p.1466)

Epidemiology

DM is a global epidemic. Type 2 DM is 10 times more frequent than type 1. Diabetic nephropathy from chronic renal failure is the most common cause of end-stage renal disease in the United States, where T2DM is overwhelmingly the primary driver. The IDF estimates hundreds of millions affected worldwide, with projections showing continued growth through 2040 across all regions, particularly Southeast Asia and the Western Pacific.

Pathophysiology

Type 1 DM

T1DM is a chronic autoimmune disease in which destruction of beta cells in the islets of Langerhans results in insulin deficiency and hyperglycemia. Markers of the immune response include:
  • Islet cell autoantibodies (ICA)
  • Autoantibodies to insulin (IAA)
  • Anti-glutamic acid decarboxylase (anti-GAD65)
  • Anti-tyrosine phosphatase-related islet antigen 2 (IA-2)
More than 60 genetic loci are associated with T1DM susceptibility, implicating the immune system. Epidemiologic evidence suggests enteroviruses as environmental triggers. T cells specific for beta-cell self-antigens cause direct tissue injury and sustain autoantibody responses until >90% of beta-cell mass is destroyed, at which point clinical hyperglycemia and ketoacidosis appear.
(Harrison's Principles of Internal Medicine 22E, p.3247; Creasy & Resnik, p.1482)

Type 2 DM

The pathophysiology involves:
  1. Peripheral insulin resistance - Target tissues (muscle, liver, adipose) fail to respond normally to insulin
  2. Progressive beta-cell failure - Initially the pancreas compensates with more insulin secretion, but over years beta-cell mass and function decline
  3. Increased hepatic glucose output - Impaired suppression of gluconeogenesis
Chronic insulin resistance takes years to decades to fully manifest. Obesity, physical inactivity, genetic predisposition, and aging are central risk factors. Insulin resistance predisposes to metabolic syndrome, prediabetes, dyslipidemia, NAFLD, and ultimately overt T2DM.
(Harrison's 22E; Mulholland & Greenfield's Surgery 7e)

Diagnosis (ADA Criteria)

Diagnosis can be established by any of four methods (requires two abnormal results unless classic symptoms + random glucose >200 mg/dL):
TestDiabetesPrediabetes (IFG/IGT)Normal
Fasting plasma glucose (FPG)≥126 mg/dL (7.0 mmol/L)100-125 mg/dL<100 mg/dL
2-hour OGTT (75g)≥200 mg/dL140-199 mg/dL<140 mg/dL
HbA1c≥6.5%5.7-6.4%<5.7%
Random plasma glucose + symptoms≥200 mg/dL--
(Tintinalli's Emergency Medicine; Goldman-Cecil Medicine; Barash's Clinical Anesthesia 9e)

Clinical Features

Symptoms of Acute Hyperglycemia

  • Polyuria - Osmotic diuresis from glycosuria
  • Polydipsia - Reactive to fluid loss
  • Polyphagia with weight loss - Inability to use glucose; protein/fat catabolism
  • Fatigue and weakness
  • Blurred vision - Osmotic lens changes (reversible with glycemic control)
  • Frequent infections - Fungal vaginitis, skin infections, poor wound healing

Signs on Physical Examination (Annual Assessment)

  • Weight and BMI
  • Retinal exam (for retinopathy)
  • Orthostatic blood pressure
  • Foot examination: pedal pulses, 10-g monofilament sensation, vibration (128-Hz tuning fork at great toe), ankle reflexes
  • Injection site inspection
  • Periodontal assessment (gum disease is more frequent in DM)
(Harrison's 22E, p.3247)

Complications

Microvascular Complications

These arise from prolonged hyperglycemia causing thickening of basement membranes and luminal narrowing of microvessels.

1. Diabetic Nephropathy (Diabetic Kidney Disease, DKD)

  • Most common cause of end-stage renal disease in the US
  • Driven by hyperglycemia and insulin resistance
  • Progresses from microalbuminuria → macroalbuminuria → declining GFR → ESRD
  • Pathology: mesangial expansion, glomerular basement membrane thickening, Kimmelstiel-Wilson nodules (nodular glomerulosclerosis)

2. Diabetic Retinopathy

  • Leading cause of blindness in working-age adults
  • Progression: nonproliferative (NPDR) → proliferative retinopathy (PDR) → vitreous hemorrhage, retinal detachment
  • Annual dilated eye exam beginning at DM diagnosis (T2DM) or 5 years after diagnosis (T1DM)

3. Diabetic Neuropathy

Occurs in ~50% of individuals with long-standing T1DM or T2DM. Risk factors: duration of diabetes, poor glycemic control, elevated BMI, smoking, hypertension, hypertriglyceridemia.
Three main forms:
a) Distal Symmetric Polyneuropathy (DSPN) - Most common form
  • Symptoms: numbness, tingling, burning, sharpness starting in feet, spreading proximally
  • Pain worse at night and at rest
  • Physical findings: reduced vibration sense, loss of ankle reflexes, 10-g monofilament insensitivity
  • Loss of protective sensation (LOPS) is major risk for foot ulceration and amputation
b) Autonomic Neuropathy
  • Cardiovascular: resting tachycardia, orthostatic hypotension, decreased heart rate variability, prolonged QTc
  • GI: gastroparesis (delayed gastric emptying), constipation, diarrhea
  • Genitourinary: neurogenic bladder, erectile dysfunction
  • Sudomotor: hyperhidrosis of upper extremities, anhidrosis of lower extremities (promotes dry cracking skin)
  • Hypoglycemia unawareness (reduced epinephrine response)
c) Mononeuropathy/Radiculopathy
  • Cranial nerve palsies (CN III, IV, VI most common), carpal tunnel syndrome, femoral neuropathy
  • Usually self-limited
(Harrison's 22E, p.1643-1659)

Macrovascular Complications

Diabetes dramatically accelerates atherosclerosis:
  • Coronary artery disease - Leading cause of mortality in T2DM; T2DM confers CAD-equivalent risk
  • Stroke - 2-4x increased risk
  • Peripheral arterial disease (PAD) - Contributes to foot ulceration and amputation
  • Insulin resistance, prediabetes, and metabolic syndrome all represent states of accelerated atherogenesis

Diabetic Foot

The combination of DSPN (loss of protective sensation), PAD (ischemia), and susceptibility to infection creates the diabetic foot syndrome - leading to ulceration and lower extremity amputation. Charcot arthropathy (neuropathic joint destruction) can also occur.

Acute Metabolic Emergencies

Diabetic Ketoacidosis (DKA)

Primarily in T1DM (can occur in T2DM). Precipitants: infection, missed insulin, new-onset DM.
Pathophysiology: Absolute insulin deficiency + excess counterregulatory hormones (glucagon, cortisol, catecholamines) → uncontrolled lipolysis → excess free fatty acids → ketogenesis (acetoacetate, beta-hydroxybutyrate) → anion gap metabolic acidosis.
Classic triad: Hyperglycemia + ketosis + metabolic acidosis
Lab findings:
  • Blood glucose typically 250-600 mg/dL
  • Anion gap metabolic acidosis (pH <7.3, HCO3 <18)
  • Ketonemia/ketonuria
  • Elevated BUN/creatinine (dehydration)
Treatment: Fluids (isotonic saline), IV insulin infusion, potassium replacement, address precipitant. Bicarbonate only if pH <6.9.

Hyperglycemic Hyperosmolar State (HHS)

Primarily in T2DM, often elderly with infection or other illness.
  • Blood glucose markedly elevated (often >600-1000 mg/dL)
  • Profound dehydration
  • High serum osmolality (>320 mOsm/kg)
  • Minimal or no ketoacidosis (enough residual insulin to suppress ketogenesis)
  • Altered consciousness is common
Treatment: Aggressive fluid replacement (more gradual than DKA), low-dose insulin, electrolyte correction.
(Goldman-Cecil Medicine; Rosen's Emergency Medicine; Symptom to Diagnosis 4e)

Management

General Goals

Goals should be individualized. The ADA recommends:
  • HbA1c target: <7% for most adults (less stringent, e.g. <8%, for elderly or those with hypoglycemia unawareness)
  • Pre-conception: HbA1c <6.5%
  • Blood pressure: <130/80 mmHg
  • LDL cholesterol: <70 mg/dL in those with ASCVD; statin therapy for most

Lifestyle (All Types)

  • Medical Nutrition Therapy (MNT): Individualized, carbohydrate-aware diet; Mediterranean and low-carbohydrate patterns have evidence
  • Exercise: Aerobic + resistance training improves insulin sensitivity and promotes weight loss; aim for 150 min/week moderate-intensity aerobic activity
  • Weight loss in T2DM: Even 5-10% weight reduction significantly improves glycemic control

Pharmacologic Management of Type 1 DM

Insulin replacement is mandatory:
PreparationOnsetPeakDuration
Rapid-acting (Aspart, Lispro, Glulisine)<0.25 h0.5-1.5 h3-5 h
Short-acting (Regular)0.5-1.0 h2-3 h4-8 h
Inhaled human insulin<0.25 h1-2 h3 h
Intermediate (NPH)2-4 h4-10 h10-16 h
Long-acting (Glargine, Detemir, Degludec)1-9 hFlat/none18-24+ h
Delivery systems: Multiple daily injections (MDI), CSII (insulin pump), sensor-augmented pump, Automated Insulin Delivery (AID/"closed-loop") systems.
(Harrison's 22E, p.1047-1090)

Pharmacologic Management of Type 2 DM

Targets different pathophysiologic processes:
Drug ClassMechanismKey Notes
Biguanides (Metformin)Reduces hepatic glucose output; improves peripheral utilizationFirst-line; weight neutral to modest loss; avoid in GFR <30, acidosis, CHF, liver disease
Sulfonylureas (Glipizide, Glimepiride, Glyburide)Stimulate insulin secretion (ATP-K+ channel)Risk of hypoglycemia; glyburide avoided in elderly
Meglitinides (Repaglinide, Nateglinide)Short-acting insulin secretagoguesTake with meals
TZDs/Thiazolidinediones (Pioglitazone)PPAR-γ agonist; increase insulin sensitivityWeight gain, fluid retention, avoid in CHF; fracture risk
DPP-4 inhibitors (Sitagliptin, Saxagliptin)Increase incretin effect; stimulate glucose-dependent insulin secretionWeight neutral; generally well tolerated
GLP-1 receptor agonists (Semaglutide, Liraglutide, Dulaglutide)Mimic GLP-1; glucose-dependent insulin release, slow gastric emptying, reduce appetiteWeight loss; CV benefits; GI side effects; injectable or oral
SGLT-2 inhibitors (Empagliflozin, Dapagliflozin, Canagliflozin)Promote urinary glucose excretionWeight loss; CV/renal benefits; risk of genital mycotic infections, DKA
InsulinDirect replacementMay be needed at any stage if severely hyperglycemic or catabolic
Key current principle: In patients with established ASCVD, heart failure, or CKD, GLP-1 agonists and SGLT-2 inhibitors are preferred beyond metformin because of proven cardiovascular and renal protection.
(Harrison's 22E, p.1131-1135)

Monitoring

  • HbA1c - Reflects average glucose over preceding 2-3 months; check every 3 months if uncontrolled, every 6 months if stable
  • Continuous Glucose Monitoring (CGM) - Real-time glucose tracking; increasingly preferred over fingerstick blood glucose monitoring (BGM)
  • Annual screening:
    • Urine albumin-to-creatinine ratio (nephropathy)
    • Dilated retinal exam (retinopathy)
    • Comprehensive foot exam (neuropathy/PAD)
    • Lipid panel
    • Serum creatinine/eGFR
    • Thyroid function (especially T1DM)
    • Vitamin B12 (if on metformin)

Special Situations

Gestational Diabetes (GDM)

  • Screen all pregnant women at 24-28 weeks with 50g GCT (or 75g OGTT by ADA criteria)
  • Diagnosed by OGTT (O'Sullivan criteria or ADA criteria)
  • Management: diet, exercise; insulin if glycemic targets not met; metformin/glyburide are used but insulin remains preferred
  • Increased risk of T2DM later in life (50% within 10 years)

Perioperative Management

  • Hold metformin on day of surgery (lactic acidosis risk, NPO status, contrast risk)
  • Hold sulfonylureas pre-op (hypoglycemia risk during fasting)
  • Insulin should be continued and carefully dosed; IV insulin infusion for major surgery
  • Target intraoperative glucose 140-180 mg/dL
(Barash's Clinical Anesthesia 9e)

Diabetic Kidney Disease (DKD) - In Depth

  • Present in approximately 20-40% of patients with DM
  • Leading cause of chronic kidney disease and ESRD globally
  • Pathology: hyperglycemia and insulin resistance drive glomerular hyperfiltration, mesangial expansion, basement membrane thickening, podocyte loss
  • Key biomarker: urine albumin (microalbuminuria = 30-300 mg/g creatinine)
  • Treatment: tight glycemic control, RAAS blockade (ACE inhibitor or ARB), SGLT-2 inhibitors (empagliflozin, canagliflozin - proven to reduce CKD progression), blood pressure control
(National Kidney Foundation Primer on Kidney Diseases 8e)

Recent Evidence (2024-2026)

  • Digital self-management interventions for T2DM (Systematic Review, J Med Internet Res, 2024): Digital interventions show modest but consistent benefit for glycemic control in T2DM. [PMID: 39037772]
  • GLP-1 agonist GI adverse events (Systematic Review, Gastroenterology, 2025): Confirms significant GI side effects (nausea, vomiting, gastroparesis risk) with GLP-1 agonists - important for clinical counseling. [PMID: 40499738]
  • Triglyceride-glucose index (Meta-Analysis, Cardiovascular Diabetology, 2024): TyG index has good diagnostic and prognostic value for insulin resistance and cardiometabolic risk. [PMID: 39180024]

Summary Table: T1DM vs T2DM

FeatureType 1 DMType 2 DM
Prevalence5-10% of DM~90% of DM
Age of onsetUsually <30, any ageUsually >40, but rising in youth
MechanismAutoimmune beta-cell destructionInsulin resistance + progressive beta-cell failure
AutoantibodiesYes (GAD, IA-2, IAA, ICA)No
KetoacidosisCommonRare (unless severe stress)
ObesityNot typicalCommon
Insulin requiredAlwaysEventually (progressive disease)
Familial clusteringModerate (HLA-linked)Strong
Key acute crisisDKAHHS
Sources: Harrison's Principles of Internal Medicine 22E (2025) | Creasy & Resnik's Maternal-Fetal Medicine | Goldman-Cecil Medicine | National Kidney Foundation Primer on Kidney Diseases 8e | Textbook of Family Medicine 9e | Rosen's Emergency Medicine | Barash's Clinical Anesthesia 9e | Ganong's Review of Medical Physiology | Basic Medical Biochemistry 6e
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