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Type 1 Diabetes Mellitus - Clinical Case Study
For exam preparation | Sources: Harrison's 22E, Goldman-Cecil Medicine, Katzung's Pharmacology 16E, Tietz Laboratory Medicine 7E, Textbook of Family Medicine 9E
PART 1 - PATIENT PRESENTATION
Patient: Maya R., 16-year-old female
Chief Complaint: 3-week history of excessive thirst, frequent urination, weight loss, and fatigue
History of Present Illness:
Maya's parents report she has been drinking large volumes of water and waking several times per night to urinate. She has lost ~5 kg over 3 weeks without dietary changes. She complains of blurred vision, persistent fatigue, and difficulty concentrating in school. Yesterday she developed nausea, vomiting, and abdominal pain. Today she is confused and her breathing is described as "deep and fast."
Past Medical History: None significant
Family History: Maternal aunt has autoimmune thyroid disease
Social History: No smoking, alcohol, or drug use
PART 2 - PHYSICAL EXAMINATION
| Finding | Detail |
|---|---|
| Temperature | 37.8°C |
| HR | 118 bpm (tachycardia) |
| BP | 95/60 mmHg (hypotension) |
| RR | 28 breaths/min (deep, labored) |
| O2 sat | 97% on room air |
| Weight | 52 kg (down from ~57 kg) |
| General | Appears ill, drowsy, dry mucous membranes |
| Breath | Fruity/acetone odor |
| Abdomen | Diffuse tenderness, no guarding |
| Neuro | GCS 13 (mild confusion) |
Key Exam Clue: The combination of polyuria, polydipsia, weight loss, Kussmaul respirations (deep, rapid), fruity breath, and altered consciousness in an adolescent is classic for new-onset T1DM presenting as DKA.
PART 3 - INVESTIGATIONS
Immediate Labs
| Test | Result | Normal |
|---|---|---|
| Blood glucose | 480 mg/dL | 70-100 mg/dL |
| Arterial pH | 7.14 | 7.35-7.45 |
| Bicarbonate | 9 mEq/L | 22-28 mEq/L |
| Anion gap | 26 mEq/L | 8-12 mEq/L |
| Serum ketones | 4+ (strongly positive) | Negative |
| Na+ | 128 mEq/L (corrected: 134) | 136-145 mEq/L |
| K+ | 5.8 mEq/L (total body K depleted) | 3.5-5.0 mEq/L |
| Creatinine | 1.3 mg/dL (pre-renal) | 0.5-1.1 mg/dL |
| HbA1c | 11.4% | <5.7% |
| C-peptide | Undetectable (<0.1 ng/mL) | 0.5-2.0 ng/mL |
| WBC | 14,500 (stress response) | 4,500-11,000 |
| Urinalysis | 4+ glucose, 3+ ketones | Negative |
Autoantibody Panel (diagnostic of T1DM)
| Antibody | Result |
|---|---|
| Anti-GAD65 | Positive |
| Insulin autoantibody (IAA) | Positive |
| Anti-ICA512 (IA-2) | Positive |
| Anti-ZnT8 | Positive |
One or more of these autoantibodies are present in 85-90% of individuals who initially experience fasting hyperglycemia from T1DM. - Textbook of Family Medicine 9E, p.985
PART 4 - DIAGNOSIS
Primary Diagnosis: Type 1 Diabetes Mellitus - new onset, presenting with Diabetic Ketoacidosis (DKA)
Diagnostic Criteria Met (ADA):
- Random plasma glucose >200 mg/dL + classic symptoms (polyuria, polydipsia, weight loss)
- HbA1c ≥6.5% (patient's is 11.4%)
- Undetectable C-peptide confirms absent endogenous insulin production
DKA Criteria Met:
- Blood glucose >250 mg/dL
- Arterial pH <7.3
- Bicarbonate <15 mEq/L
- Elevated anion gap (26 mEq/L)
- Positive serum/urine ketones
Classification: Severe DKA (pH <7.1)
Pathophysiology - Why Did This Happen?
T1DM results from cellular-mediated autoimmune destruction of pancreatic beta cells. This is classified as T1a (immune-mediated), the most common form. The process involves:
- Genetic susceptibility (HLA-DR3/DR4 haplotypes, multigenic)
- Environmental trigger (possibly viral - Coxsackievirus, enterovirus)
- Autoimmune response: T lymphocytes attack beta cells; autoantibodies (GAD65, IAA, IA-2, ZnT8) are generated
- Progressive beta cell loss -> absolute insulin deficiency
- Without insulin: unrestrained gluconeogenesis, glycogenolysis, lipolysis -> hyperglycemia + ketonemia -> DKA
"The immune form is the most common form of type 1 diabetes. Although most patients are younger than 30 years of age at the time of diagnosis, the onset can occur at any age." - Katzung's Pharmacology 16E
Worldwide, between 13% and 80% of individuals with type 1 diabetes present initially with DKA. DKA at diagnosis is more common in children younger than 5 years and in those without access to medical care. - Goldman-Cecil Medicine
PART 5 - MANAGEMENT
Phase 1: Emergency Management of DKA
ABC + IV Access (2 large-bore IVs)
Step 1 - Fluid Resuscitation (MOST IMPORTANT first step)
- 0.9% NaCl: 1 L bolus over 1 hour, then 500 mL/hr for 2-4 hours
- Then transition to 0.45% NaCl at 250-500 mL/hr as glucose falls
- Add D5W when glucose reaches 200-250 mg/dL (prevents hypoglycemia while continuing insulin)
Step 2 - Insulin Therapy
- Do NOT start insulin until K+ ≥3.5 mEq/L (insulin drives K+ into cells - risk of fatal arrhythmia)
- Regular insulin IV infusion: 0.1 units/kg/hr (= 5.2 units/hr for this patient)
- Target glucose reduction: 50-75 mg/dL per hour
- Do NOT drop glucose too fast - risk of cerebral edema (especially in children/adolescents)
Step 3 - Potassium Replacement (critical)
- Despite serum K+ of 5.8, total body K is depleted (lost via osmotic diuresis)
- Once urine output confirmed and K+ <5.5: add 20-40 mEq KCl per liter of IV fluid
- Goal K+: 4.0-5.0 mEq/L
- Monitor every 1-2 hours
Step 4 - Bicarbonate (controversial)
- Generally NOT given unless pH <6.9 or life-threatening hyperkalemia
- Risk of paradoxical CNS acidosis and hypokalemia
Monitoring: Glucose hourly, electrolytes/pH every 2-4 hours, continuous cardiac monitoring
Criteria to Transition to Subcutaneous Insulin:
- pH >7.3, bicarbonate >18, anion gap closed (<12)
- Patient eating and tolerating oral intake
- Overlap subcutaneous long-acting insulin by 2 hours before stopping IV drip
Phase 2: Long-Term Insulin Therapy
Principle: Mimic physiologic insulin secretion with a basal-bolus regimen
"The goal is to design and implement an insulin regimen that mimics physiologic insulin secretion. Because individuals with type 1 DM partially or completely lack endogenous insulin production, administration of basal insulin is essential." - Harrison's Principles of Internal Medicine 22E
Insulin Types (Key Table for Exams)
| Preparation | Onset | Peak | Duration |
|---|---|---|---|
| Rapid-acting (Aspart, Lispro, Glulisine) | <15 min | 0.5-1.5 h | 3-5 h |
| Short-acting (Regular) | 30-60 min | 2-3 h | 4-8 h |
| Intermediate (NPH) | 2-4 h | 4-10 h | 10-16 h |
| Long-acting (Glargine, Detemir) | 1-4 h | Flat (no peak) | 20-24 h |
| Ultra-long-acting (Degludec) | 1-9 h | Flat | >42 h |
(Source: Harrison's 22E)
Regimen Options (in order of preference):
- AID (Automated Insulin Delivery) - PREFERRED for most T1DM patients: insulin pump + continuous glucose monitor (CGM) + closed-loop algorithm automatically adjusts basal rate
- CSII (Insulin Pump): Continuous basal infusion + patient-directed boluses before meals
- MDI (Multiple Daily Injections): Long-acting basal once daily + rapid-acting bolus before each meal
"AID is the preferred insulin delivery mechanism for most individuals with type 1 DM." - Harrison's 22E
Typical Starting Doses (MDI):
- Total daily dose: ~0.5 units/kg/day
- 50% as basal (long-acting): ~13 units glargine at bedtime
- 50% as bolus (rapid-acting): ~4 units aspart before each main meal, adjusted for carbohydrate count (typical ratio: 1 unit per 10-15g carbohydrate)
Phase 3: Monitoring and Targets
| Parameter | Target |
|---|---|
| HbA1c | <7.0% (general); may relax to <7.5% in young children |
| Fasting glucose | 80-130 mg/dL |
| Peak postprandial glucose (1-2h after meal) | <180 mg/dL |
| Time in Range (CGM, 70-180 mg/dL) | >70% |
| Time below range (<70 mg/dL) | <4% |
The DCCT (1993) - a landmark multicenter RCT in 1441 T1DM patients - showed that intensive insulin therapy reduces the risk of retinopathy, nephropathy, and neuropathy by 40-75% compared to conventional therapy. The benefit persisted for 19+ years (metabolic memory). - Tietz Laboratory Medicine 7E
PART 6 - COMPLICATIONS (for exam MCQs)
Acute Complications
| Complication | Trigger | Key Features |
|---|---|---|
| DKA | Illness, missed insulin, new onset | pH <7.3, ketones +, anion gap ↑, glucose >250 |
| Hypoglycemia | Excess insulin, missed meal, exercise | Glucose <70; treat with 15g fast-acting carbs (rule of 15) |
| Somogyi effect | Rebound hyperglycemia after nocturnal hypoglycemia | High AM glucose; reduce evening insulin |
| Dawn phenomenon | Growth hormone surge 3-8 AM | High fasting glucose without nocturnal hypo; increase basal insulin |
Chronic Complications (microvascular)
- Diabetic Retinopathy - most common cause of new blindness in working-age adults; background (non-proliferative) -> proliferative (neovascularization)
- Diabetic Nephropathy - begins as microalbuminuria (30-300 mg/day); progresses to macroalbuminuria -> ESRD; screen with uACR annually
- Diabetic Neuropathy - distal symmetric polyneuropathy (stocking-glove pattern); autonomic neuropathy (gastroparesis, orthostatic hypotension, erectile dysfunction)
Chronic Complications (macrovascular)
- Accelerated atherosclerosis: coronary artery disease, stroke, peripheral vascular disease
- DCCT showed 42% lower CVD incidence in intensively treated group at 17-year follow-up
Associated Autoimmune Conditions (screening required at T1DM diagnosis)
| Condition | Prevalence in T1DM | Screening Test |
|---|---|---|
| Autoimmune thyroid disease | 15-30% | Thyroid peroxidase antibodies |
| Celiac disease | 4-9% | Tissue transglutaminase IgA |
| Addison disease | ~0.5% | 21-hydroxylase antibodies |
"33% of patients with T1DM screen positive for at least one additional organ-specific autoantibody when initially diagnosed." - Textbook of Family Medicine 9E
PART 7 - SPECIAL CONSIDERATIONS
"Honeymoon Phase"
After initiating insulin therapy, many patients experience weeks to months of easily controlled hyperglycemia as stress resolves and residual beta cells resume some function. Insulin requirements fall transiently. This does NOT mean T1DM is gone - the autoimmune destruction continues. Parents and patients must be warned not to stop insulin.
LADA (Latent Autoimmune Diabetes in Adults)
A slower autoimmune form of T1DM. Up to 10-15% of adults diagnosed with "Type 2" may actually have LADA. Features: lean body habitus, antibody-positive (especially anti-GAD65), initially responds to oral agents, eventually becomes fully insulin-dependent.
Teplizumab (new disease-modifying therapy)
A humanized anti-CD3 monoclonal antibody approved (FDA 2022) for stage 2 T1DM (two positive autoantibodies + impaired glucose tolerance) in patients age 8+. Given as a 14-day IV infusion. Delays progression to clinical T1DM (stage 3) by approximately 25 months. - Katzung's 16E
Type 1B (Idiopathic) Diabetes
- Antibody-negative T1DM, not immune-mediated
- More common in patients of African or Asian ancestry
- Insulin-requiring but mechanism is non-autoimmune
PART 8 - EXAM SUMMARY / HIGH-YIELD POINTS
| Concept | Key Fact |
|---|---|
| Autoantibodies | GAD65, IAA, IA-2, ZnT8 - present in 85-90% at diagnosis |
| C-peptide | Undetectable in T1DM (measures endogenous insulin) |
| HbA1c target | <7.0% (ADA) |
| First step in DKA | IV fluids (not insulin) |
| Insulin before K+ | Never start insulin if K+ <3.5 (arrhythmia risk) |
| DCCT | Intensive therapy reduces micro-complications 40-75% |
| Metabolic memory | Benefits of early tight control persist for 19+ years |
| Teplizumab | Anti-CD3; delays T1DM onset by ~25 months |
| Honeymoon phase | Temporary - do not stop insulin |
| Most common assoc. condition | Autoimmune thyroid disease (15-30%) |
| Kussmaul breathing | Deep, sighing respirations - compensatory for metabolic acidosis |
| Fruity breath | Exhaled acetone from ketones |
Sources:
- Harrison's Principles of Internal Medicine 22E (2025) - insulin delivery systems, AID, complications management
- Goldman-Cecil Medicine - clinical presentation, DKA, honeymoon phase
- Katzung's Basic and Clinical Pharmacology 16E - T1DM pathogenesis, teplizumab, insulin types
- Tietz Textbook of Laboratory Medicine 7E - autoantibodies, DCCT evidence, HbA1c
- Textbook of Family Medicine 9E - C-peptide, associated autoimmune conditions, LADA
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