Equis ISSN 2398-2977

Pancreas: hyperinsulinemia

Contributor(s): David Moll, Graham Munroe, Janice Sojka

Introduction

  • Very rare, however high insulin due to insulin resistance (both idiopathic, ie equine metabolic syndrome   Equine metabolic syndrome  , and secondary to other endocrinopathy such as pituitary pars intermedia dysfunction) is fairly common.
  • Cause: secondary to increased release of insulin by a pancreatic tumor, or therapeutic/misuse injection of insulin   Protamine zinc insulin  . While specific cause of idiopathic hyperinsulinemia is not known, it is most common in ponies and other "thrifty" breeds such as Morgan. Insulin resistance secondary to endocrinopathy most commonly caused by presence of a pituitary tumor   Pituitary: adenoma  .
  • Signs:
    • If no insulin resistance - hypoglycemia   Hypoglycemia  , ie ataxia, disorientation, recumbency, seizures, coma, death.
    • With insulin resistance - obesity, abnormal fat distribution, infertility and laminitis are the most common clinical signs.
  • Diagnosis: glucose assay   Blood: biochemistry - glucose  (hypoglycemia), high pressure liquid chromatography (exogenous or endogenous insulin), laparoscopy   Abdomen: laparoscopy  /exploratory laparotomy   Abdomen: laparotomy   +  pancreatic biopsy (tumor identification)   Biopsy: overview  .
  • Insulin resistance is diagnosed via measuring glucose/insulin ratio or via glucose tolerance testing.
  • Treatment: none for primary hyperinsulinemia; low carbohydrate diet and thyroxine used to treat secondary hyperinsulinemia.
  • Prognosis: grave for primary hyperinsulinemia; fair for secondary hyperinsulinemia.

Pathogenesis

Etiology

  • Pancreatic neoplasia, therapeutic injection or misuse of insulin   Protamine zinc insulin  , eg where animals are insured against death.
  • Hormone secreting tumors that produce substances that are insulin antagonists require pancreas to secrete more than normal amounts of insulin in order to maintain normoglycemia.
  • Etiology of equine metabolic syndrome   Equine metabolic syndrome   not known.

Specific

  • Pancreatic adenoma.
  • Pancreatic adenocarcinoma.
  • Insulin overdose   Protamine zinc insulin  .
  • Pars intermedia tumor.

Pathophysiology

  • Pancreatic tumor    →   insulin release   →    hypoglycemia   →    clinical signs (severity depends on degree of hypoglycemia and can fluctuate with feeding).
  • Development of the tumor is usually slow and associated with other non-specific clinical signs of chronic pancreatic disease.
  • Adenocarcinoma may occlude the common bile duct   →    cholestasis   →    severe liver dysfunction.
  • Insulin overdose   →    sudden massive hypoglycemia   →    collapse/death.
  • Pituitary tumor   →    increased serum cortisol   →    hyperglycemia   →    feedback to pancreas   →    increased insulin secretion.
  • Peripheral insulin resistance   →    hyperglycemia   →    feedback to pancreas   →    increased insulin secretion.

Timecourse

  • Tumor development is usually gradual and symptoms are episodic.
  • Insulin resistance is usually gradual and may be seasonal; problems worse in autumn when ACTH levels increased   →    higher peripheral levels of cortisol, an insulin antagonist.
  • Insulin overdose   →    rapid onset of symptoms.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Carter R A, Treiber K H, Geor R J, Douglass L & Harris P A (2009) Prediction of incipient pasture-associated laminitis from hyperinsulinaemia, hyperleptinaemia and generalised localised obesity in a cohort of ponies. Equine Vet J 41 (2), 171-178 PubMed.
  • Johnson P J, Wiedmyeyer C E & Messer N T (2009) Conditions of the equine pancreas. Equine Vet Educ 21 (1), 26-29 VetMedResource.
  • Fishman A M & Valberg S J (2007) Factors affecting clinical assessment of insulin sensitivity in horses. Equine Vet J 39, 567-575 PubMed.

Other sources of information

  • Reed S M, Bayly W M & Sellon D C (2004) Equine Internal Medicine. 2nd edn. W B Saunders. ISBN: 0721697771.
  • Brown C M & Bertone J J (2002) The 5-Minute Veterinary Consult Equine. Lippincott, Williams & Wilkins. ISBN: 0683306057.
  • Mair T, Divers T & Ducharme N (2002) Manual of Equine Gastroenterology. W B Saunders. ISBN: 0702024864.


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