Hypopituitarism in Dogs
Hypopituitarism in dogs is a condition characterized by the inadequate production of various hormones by the pituitary gland, a small endocrine gland located at the base of the brain near the hypothalamus. The deficiency of hormones such as thyroid-stimulating hormone (TSH), adrenocorticotropin hormone (which stimulates the adrenal cortex), luteinizing hormone (involved in sex steroid secretion), follicle-stimulating hormone (important for gonadal function), and growth hormone (GH) can lead to significant clinical implications.
This disorder typically manifests in dogs between the ages of two to six months. Certain breeds, including German shepherds, Carnelian bear dogs, spitzes, toy pinschers, and weimaraners, appear to have a predisposition to hypopituitarism. In German shepherds and Carnelian bear dogs, a simple autosomal recessive genetic trait has been identified as a causative factor for this condition.
The onset of hypopituitarism can be attributed to various factors such as cancerous growths, degenerative processes, or anomalies that affect the pituitary gland, leading to its destruction.
Symptoms
Symptoms of hypopituitarism can vary depending on which hormones are lacking and which bodily functions are affected. For instance, a deficiency in luteinizing hormones may lead to sexual abnormalities like abnormally small genitals, while a lack of growth hormone (GH) can result in insufficient growth or dwarfism. If the gland is affected by cancer or a tumor, the affected individual may experience head pain (resulting in head-pressing) or visual problems. Additional symptoms may include:
- Difficulty in house-breaking, indicative of mental retardation
- Thin, hypotonic skin, characterized by reduced muscle or artery tone
- Trunk hair loss (alopecia)
- Cutaneous hyperpigmentation, leading to darkened skin areas
- Delayed dental eruption
- Head-pressing due to head pain from a tumor
Causes
Causes of hypopituitarism can be categorized as congenital or acquired. Congenital factors include:
- Cystic Rathke’s pouch: This refers to a benign cystic tumor that develops from remnants of fetal tissue.
- Isolated GH (growth hormone) deficiency: A condition where there is a lack of growth hormone.
- Pituitary tumor: The presence of a tumor in the pituitary gland.
Acquired causes include:
- Trauma: Instances of physical injury leading to hypopituitarism.
- Radiotherapy: Treatment involving the use of radiation as a potential cause for the condition.
Diagnosis
To diagnose hypopituitarism in your dog, your veterinarian will conduct a comprehensive assessment of its health history, growth patterns, behavioral development, symptom onset, and any potential incidents such as head trauma. The diagnostic process involves a series of tests including:
- A complete blood profile comprising a chemical blood profile, complete blood count, and urinalysis. Blood tests are crucial for accurate diagnosis.
- Standard blood test results may reveal elevated levels of eosinophilia (white blood cells), lymphocytosis (lymph gland disorder), hypophosphatemia (phosphorus deficiency), or hypoglycemia (low blood sugar).
- Additional laboratory tests will assess hormone levels in the bloodstream. A morning blood draw is typically conducted to measure basal levels of TSH and prolactin. Dynamic tests involve measuring hormone levels after administering a stimulating substance, which helps evaluate ACTH and GH levels.
- Visual imaging techniques, primarily X-ray, are utilized to identify the presence of tumors or cysts near the pituitary gland.
These diagnostic procedures collectively provide valuable insights into the presence and extent of hypopituitarism in your dog.
Treatment
Treatment for hypopituitarism typically occurs on an outpatient basis. Your dog will receive growth hormone supplements three times a week for 4–6 weeks, with the possibility of repetition if needed. In certain instances, surgical removal of pituitary gland tumors is feasible, although the prognosis is generally guarded.
Living and Management
In managing your dog’s condition, your veterinarian will schedule regular follow-up appointments to monitor blood and urinary glucose levels. If glucosuria (excretion of glucose by the kidneys) develops or if blood glucose exceeds 150 mg/dL, growth hormone supplementation may be paused.
Improvements in your dog’s skin and haircoat should be noticeable within 6–8 weeks of starting growth hormone and thyroid supplementation. Typically, if growth hormone levels are low, there won’t be a significant increase in stature since the growth plates usually close by the time of diagnosis. Unfortunately, since many hormones affected by pituitary disorders are vital for overall health, the long-term prognosis for hypopituitarism remains poor.