Autoimmune destruction of pancreatic beta cells leading to absolute insulin deficiency.
Also known as: T1DM, type 1 diabetes, insulin-dependent diabetes, juvenile diabetes, IDDM
Overview
Chronic autoimmune disease characterized by T-cell mediated destruction of pancreatic islet beta cells, resulting in absolute insulin deficiency and lifelong dependence on exogenous insulin to prevent ketoacidosis and death.
Epidemiology
Accounts for ~5-10% of all diabetes. Bimodal peak incidence at age 4-7 and 10-14 years, but can present at any age (including LADA in adults). Higher prevalence in non-Hispanic whites, Scandinavian populations. Strong HLA association (HLA-DR3, HLA-DR4).
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Genetic: HLA-DR3/DR4-DQ8 haplotypes (highest risk), family history (5-10% if first-degree relative)
Environmental triggers: enteroviral infection (coxsackie B), early cow's milk exposure, vitamin D deficiency
Other autoimmune disease: Hashimoto thyroiditis, celiac disease, Addison disease, pernicious anemia (polyglandular syndrome type 2)
Pathophysiology
Autoreactive T cells infiltrate pancreatic islets (insulitis) and selectively destroy insulin-producing beta cells. Clinical hyperglycemia emerges when ~80-90% of beta-cell mass is lost. Absolute insulin deficiency leads to unopposed glucagon action, hepatic gluconeogenesis, lipolysis, and ketogenesis. Without insulin, patients cannot suppress ketone production and are at risk for DKA.
Clinical presentation
Symptoms
Classic triad: polyuria, polydipsia, polyphagia
Unintentional weight loss despite normal or increased intake
Fatigue, weakness, blurred vision
May present with DKA as initial manifestation (~30% of pediatric cases): nausea, vomiting, abdominal pain, Kussmaul respirations, altered mental status
Lean young patient with rapid onset of polyuria, polydipsia, weight loss, sometimes presenting in DKA.
Differential diagnosis
Type 2 diabetes mellitus — Older onset, obesity, acanthosis nigricans, family history, gradual onset; insulin resistance with relative deficiency; negative autoantibodies; C-peptide preserved
Latent autoimmune diabetes of adults (LADA) — Adult onset (>30), initial response to oral agents then rapid progression to insulin; positive GAD-65 antibodies; slow autoimmune destruction
MODY (maturity-onset diabetes of the young) — Autosomal dominant family history across 3 generations; onset <25; non-obese; no autoantibodies; preserved C-peptide; HNF1A/glucokinase mutations
Secondary diabetes (pancreatic) — History of chronic pancreatitis, pancreatectomy, hemochromatosis, cystic fibrosis; absent C-peptide; pancreatic exocrine insufficiency
Honeymoon phase: transient partial remission after diagnosis with reduced insulin requirements; insulin needs return as residual beta cells fail.
Dawn phenomenon: early morning hyperglycemia from nocturnal growth hormone and cortisol surge; treat by adjusting basal insulin timing.
Somogyi effect: rebound hyperglycemia after nocturnal hypoglycemia (controversial in modern practice with CGM data).
Always check for DKA in any T1DM patient with acute illness, vomiting, or hyperglycemia >250 mg/dL.
Sick-day rules: never stop insulin; check ketones; increase frequency of glucose monitoring; maintain hydration.
References
ADA 2025 — American Diabetes Association Standards of Care in Diabetes—2025 (Diabetes Care 2025; 48 Suppl 1)
DCCT/EDIC — The Effect of Intensive Treatment of Diabetes on the Development and Progression of Long-Term Complications in IDDM (DCCT Research Group, NEJM 1993)
ISPAD 2022 — ISPAD Clinical Practice Consensus Guidelines 2022 — Type 1 Diabetes in Children and Adolescents
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