Diabetes Mellitus for USMLE Step 2

Diabetes Mellitus for the USMLE Step 2 Exam

Diabetes Mellitus (DM) is characterized by chronic hyperglycemia due to defects in insulin production, insulin action, or both.

Type 1 Diabetes Mellitus (T1DM): An autoimmune disorder leading to the destruction of pancreatic beta cells, resulting in absolute insulin deficiency. Most often presents in childhood or adolescence.
Type 2 Diabetes Mellitus (T2DM): Characterized by insulin resistance and relative insulin deficiency. Initially, the pancreas compensates by increasing insulin secretion, but over time, beta-cell dysfunction leads to chronic hyperglycemia. T2DM is associated with obesity and lifestyle factors.
Gestational Diabetes Mellitus (GDM): Diabetes diagnosed during pregnancy, which increases the risk of T2DM in the mother postpartum.

T1DM: Presents with polyuria, polydipsia, polyphagia, and weight loss due to absolute insulin deficiency. If untreated, it can progress to diabetic ketoacidosis (DKA).
T2DM: Often asymptomatic in the early stages and diagnosed through routine screening or after the onset of complications. Symptoms may include polyuria, fatigue, recurrent infections, and blurred vision.
Diabetic Ketoacidosis (DKA): An acute complication of T1DM characterized by hyperglycemia, ketosis, and metabolic acidosis. Symptoms include vomiting, abdominal pain, dehydration, and altered mental status.
Hyperosmolar Hyperglycemic State (HHS): A complication of T2DM that presents with severe hyperglycemia, dehydration, and altered consciousness but lacks significant ketosis.

Diagnostic Criteria (ADA):
Fasting plasma glucose (FPG) ≥126 mg/dL.
2-hour plasma glucose ≥200 mg/dL during a 75 g oral glucose tolerance test (OGTT).
Hemoglobin A1c (HbA1c) ≥6.5%.
Random plasma glucose ≥200 mg/dL with classic symptoms of hyperglycemia (polyuria, polydipsia, and weight loss).
Screening: Adults aged ≥45 should be screened every 3 years or earlier in patients with risk factors such as obesity, family history of diabetes, or a history of GDM.

Non-Pharmacologic Management:
Lifestyle Modifications: Essential for managing both T1DM and T2DM. This includes dietary adjustments (monitoring carbohydrate intake, increasing fiber), regular physical activity (at least 150 minutes of moderate exercise per week), and weight management in T2DM.
Pharmacologic Management:
Type 1 Diabetes: Insulin is the mainstay of treatment. Multiple daily insulin injections (basal-bolus regimen) or continuous subcutaneous insulin infusion (CSII) via insulin pumps are commonly used.
Type 2 Diabetes:
Metformin: First-line therapy. It decreases hepatic gluconeogenesis and improves insulin sensitivity.
Second-Line Agents:
GLP-1 Receptor Agonists: Improve glycemic control and promote weight loss.
SGLT-2 Inhibitors: Lower blood glucose by increasing glucose excretion in urine and provide cardiovascular and renal protection.
DPP-4 Inhibitors: Increase insulin secretion and decrease glucagon secretion.
Insulin: Used in T2DM when oral agents or non-insulin injectables are inadequate or in cases of severe hyperglycemia.

Microvascular Complications:
Diabetic Retinopathy: Can lead to blindness. Patients should undergo annual ophthalmologic exams.
Diabetic Nephropathy: Screening for albuminuria is essential. Uncontrolled diabetes may lead to end-stage renal disease (ESRD).
Diabetic Neuropathy: Peripheral neuropathy causes numbness and pain, typically in the feet. Autonomic neuropathy can affect gastrointestinal motility and cause cardiovascular instability.
Macrovascular Complications:
Cardiovascular Disease (CVD): Diabetes increases the risk for coronary artery disease, stroke, and peripheral artery disease (PAD).
Acute Complications:
DKA: Common in T1DM and can be life-threatening if untreated. Treatment includes IV fluids, insulin, and electrolyte management.
HHS: Seen in T2DM and requires aggressive rehydration and insulin therapy.

Key Points

Pathophysiology: T1DM results from autoimmune destruction of beta cells, causing absolute insulin deficiency. T2DM involves insulin resistance and relative insulin deficiency, often related to obesity and sedentary lifestyle.
Diagnosis: ADA diagnostic criteria include FPG ≥126 mg/dL, 2-hour OGTT ≥200 mg/dL, HbA1c ≥6.5%, or random glucose ≥200 mg/dL with symptoms.
Management: T1DM requires insulin therapy. T2DM is managed with lifestyle changes and medications like metformin, GLP-1 agonists, SGLT-2 inhibitors, and insulin in advanced cases.
Complications: Microvascular complications include retinopathy, nephropathy, and neuropathy. Macrovascular complications include CVD. Acute complications include DKA and HHS.