Puerperal hypocalcemia

From Dog
Milkfever01.jpg

Puerperal hypocalcemia (milk fever; eclampsia; puerperal hypocalcemia) is a common post-whelping disorder of dogs characterized by hypocalcemia-related fever and neurological disease[1].

This disorder manifests 2 - 3 weeks post-whelping as an acute, life-threatening condition, with small-breed bitches with large litters predisposed. Hypocalcemia may also occur during parturition and may precipitate dystocia.

Puerperal hypocalcemia results from excessive mammary gland loss of calcium via milk exacerbated by inadequate dietary calcium intake and poor calcium mobilization from bone, causing circulatory hypocalcemia[2].

Although the incidence is higher in small breeds of dogs, it can occur in any breed of dog, with any size litter, and at any time during lactation. Rarely, it occurs during late gestation in bitches. Although uncommon in queens, it may occur during early lactation.

Hypocalcemia, which is the primary humoral manifestation of this disease, occurs when blood ionized calcium (iCa) level falls below 6.5 mg/dL (< 1.25 mmol/L) (normal 9 - 11.4 mg/dL).

Serum total calcium does not accurately predict ionized calcium status in many clinical conditions[3]. Calcium homeostasis in hypoalbuminemic critically ill dogs should be evaluated by iCa concentrations rather than total calcium or calcium adjusted for albumin or total protein[4].

In dogs with hypocalcemia, the low concentration of calcium causes an excitatory effect on nerve and muscle cells, lowering the threshold potential and discharging repetitively without provocation. Tetany occurs as a result of spontaneous repetitive firing of motor nerve fibers. Hypoglycemia can occur concurrently in these bitches.

Clinically symptoms may be subtle, but common signs include restlessness, fever (variable), twitching and behavioral changes. In severe cases, seizures, coma and death may ensue.

Diagnosis is readily achieved based on historical evidence of recent whelping, hypocalcemia, hypophosphatemia and clinical signs of muscular tremors.

Electrocardiographs usually reveal prolonged QT intervals and premature ventricular complexes.

Differential diagnoses include other causes of seizures such as hypoglycemia, toxins, idiopathic epilepsy or meningoencephalitis.

Treatment is usually effective with intravenous calcium gluconate given slowly to effect (0.5 – 1.5 mL/kg over 10 – 30 minutes; 5 – 20 mL total), followed by oral calcium supplementation and immediate weaning of pups. Affected bitches are at risk of redeveloping eclampsia in subsequent pregnancies.

Dihydrotachysterol and vitamin D (0.03 – 0.06 μg/kg/day) supplementation may also be used.

Corticosteroids lower serum calcium and, therefore, are contraindicated. They may interfere with intestinal calcium transport and increase urinary loss of calcium.

References

  1. Drobatz KJ & Casey KK (2000) Eclampsia in dogs: 31 cases (1995-1998). J Am Vet Med Assoc 217(2):216-219
  2. Chastain CB et al (1999) Serum electrolyte concentrations in bitches with eclampsia. Vet Rec 145(11):318–320
  3. Schenck PA & Chew DJ (2008) Calcium: total or ionized? Vet Clin North Am Small Anim Pract 38(3):497-502
  4. Sharp CR et al (2009) A comparison of total calcium, corrected calcium, and ionized calcium concentrations as indicators of calcium homeostasis among hypoalbuminemic dogs requiring intensive care. J Vet Emerg Crit Care (San Antonio) 19(6):571-578