Diabetes mellitus

Diabetes mellitus, often referred to simply as diabetes, is a group of metabolic conditions characterized by hyperglycemia. 

These conditions should not be confused with diabetes insipidus which is clinically distinct and not related to hyperglycemia.

Symptoms/signs of hyperglycemia classically include 1,2:

  • polyuria: frequent urination
  • polydipsia: increased thirst
  • hunger
  • fatigue
  • weight loss (often masked by being overweight)

Other manifestations include:

  • diabetic dermopathy: e.g. granuloma annulare, necrobiosis lipoidica diabeteticorum, eruptive xanthoma, and acanthosis nigricans 3
  • diabetic mastopathy (benign tumor like breast masses)
  • manifestations of complications (see below)

There are many forms of diabetes mellitus:

  • type 1 diabetes mellitus
    • the result of failure of pancreatic insulin production due to loss of beta cells in the pancreatic islets 1
    • the etiology of this process is unknown but thought to be autoimmune 1
  • type 2 diabetes mellitus
    • the result of increasing insulin resistance, where the body's cells do not respond sufficiently to produced insulin 2
    • this is the most common form of diabetes mellitus (accounts for 90%) and is generally the result of obesity and occurs as part of the metabolic syndrome 2
  • ​gestational diabetes
    • hyperglycemia occurring in pregnant women without a prior history of diabetes 7
  • maturity onset diabetes of the young (MODY)
    • a rarer form of diabetes that is the result of one of a number of single-gene mutations causing defects in insulin production 8
    • there are a number of subtypes and these are generally inherited in an autosomal dominant manner 8
  • latent autoimmune diabetes of adults (LADA)
    • also known as diabetes mellitus 1.5 9
    • refers to the situation in which type 1 diabetes mellitus develops in adults 9
    • this may initially be mistaken for type 2 diabetes mellitus 9

Additionally, patients can be described as having 'prediabetes': a term used to describe the situation where an individual may have elevated glucose levels but does not reach diabetic diagnostic criteria. This includes the concepts of impaired fasting glucose and impaired glucose tolerance.

The diagnosis of diabetes mellitus, generally, requires 1,2:

  • 2-hour glucose (glucose tolerance test) ≥11.1 mmol/L
  • fasting glucose ≥7.0 mmol/L
  • HbA1c ≥6.5% or ≥48 mmol/mol

In type 1 diabetes mellitus, for example, there are additional tests utilized to confirm the diagnosis, such as detection of autoantibodies (e.g. anti-GAD antibodies, anti-tyrosine phosphatase IA2 antibodies, anti-insulin antibodies) and C-peptide 1.

The hyperglycemia that characterizes diabetes mellitus is clearly not radiographically visible but the complications of diabetes can often be detected radiologically, including (but not limited to) 10,11:

Furthermore, given the higher risk of infection seen in diabetes mellitus, these are also more likely to seen radiographically in diabetic patients (e.g. osteomyelitisemphysematous pyelonephritis) 10

Treatment options vary depending on the type of diabetes, however the following are the general options available 1,2,12:

  • lifestyle interventions
    • e.g. diabetes education, weight management, appropriate diet, aerobic exercise, cessation of smoking and alcoholism
    • these are generally indicated in patients with type 2 diabetes mellitus
  • antihyperglycaemic therapy
    • oral therapy (generally indicated in patients with type 2 diabetes mellitus)
      • biguanides (e.g. metformin)
      • sulfonylureas (e.g. gliclazide)
      • dipeptidyl peptidase-4 (DPP-4) inhibitors (e.g. linagliptin)
      • thiazolidinediones (e.g. pioglitazone)
      • sodium glucose co-transporter 2 (SGLT2) inhibitor (e.g. dapagliflozin)
      • alpha-glucosidase inhibitor (e.g. acarbose)
    • insulin therapy (indicated in those with type 1 diabetes mellitus and in type 2 diabetes mellitus refractory to oral therapy)
      • many different forms (e.g. ultra-short acting, short-acting, long-acting, ultra-long-acting) and regimens
      • often used concurrently with oral therapy in patients with type 2 diabetes mellitus
    • glucagon-like peptide-1 (GLP-1) receptor analogs (e.g. exenatide), these medications are administered subcutaneously
  • bariatric surgery

Complications to the disease process can be either acute or chronic:

  • acute complications include:
    • diabetic ketoacidosis 4
      • a potentially life-threatening condition characterized by significantly elevated blood glucose, low blood pH and ketones in the blood or urine
      • nearly always only seen in patients with type 1 diabetes mellitus, often at time of diagnosis
      • however, diabetic ketoacidosis can also occur in type 1 diabetic patients with poor control or if they have not taken their normal insulin
    • hyperosmolar hyperglycemic state 5
      • extremely high blood glucose and high blood osmolarity are seen but significant ketoacidosis is generally not a feature
      • has neurological manifestations such as hemichorea and seizures
      • seen most commonly in patients with type 2 diabetes mellitus
    • higher risk of infections
  • chronic complications of diabetes are protean and broadly include 1,2,6:

Furthermore, each therapy has its own potential set of complications, the most common and serious complication being hypoglycemia.

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Article information

rID: 64064
Synonyms or Alternate Spellings:
  • type 2 diabetes mellitus
  • type 1 diabetes mellitus
  • type 1 diabetes
  • type 2 diabetes
  • diabetes

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Cases and figures

  • Case 1: with diabetic foot
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  • Case 2: with diabetic foot and osteomyelitis
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  • Case 3: with diabetic mastopathy
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  • Case 4: with diabetic myonecrosis
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  • Case 5: with vas deferens calcification
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  • Case 6: with arterial calcifications
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  • Case 7: with emphysematous pyelonephritis
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  • Case 8: with Fournier gangrene
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