Dwarfism (Hypopituitarism) in Dogs
Overview of Canine Dwarfism (Hypopituitarism)
Dwarfism develops in young dogs from a deficiency of growth hormone (GH), which is normally secreted by the pituitary gland. Dwarfism is sometimes a component of hypopituitarism, in which one or more of the pituitary hormones are not produced in normal amounts.
The inherited form of dwarfism is believed to be a simple autosomal recessive trait in the German shepherd dog and Carnelian/Karelian bear dog. With recessive genetic traits the condition only becomes apparent when the puppy receives one defective gene from both parents. Dwarfism develops when two defective genes are present together. When only one defective gene occurs, the dog is a carrier of the condition, but does not show any signs of dwarfism. Although dwarfism is most common in the German shepherd dog, it has also been reported in the spitz, toy pinscher, and some Weimaraners.
Dwarfism may also arise with developmental abnormalities of the pituitary gland. If the pituitary gland fails to develop normally, if cysts occur, or if the gland is affected by benign enlarging tumors, then growth hormone production may be decreased or absent.
These dogs appear normal at birth, but show evidence of failure to grow by two to three months of age. Unlike chondrodystrophic (skeletal) dwarfs, pituitary dwarf dogs have normal proportionate sizes to their limbs, trunk and other body structures. They are simply smaller than expected.
What to Watch For
Symptoms of dwarfism in dogs may include:
- Short stature compared to littermates
- Soft wooly hair coat, retention of puppy coat
- Gradual development of alopecia (hair loss)
- Sparing the head and limbs
- Hyperpigmentation (darkening) of the skin
- Delayed eruption or absence of permanent teeth
- A shrill bark
- Small testicles and sometimes infertility in the male
- Absent estrus (heat) and sometimes infertility in the female
Diagnosis of Dwarfism in Dogs
A presumptive diagnosis is based on breed, history, and clinical signs. Your veterinarian may also recommend the following diagnostic tests:
- Baseline tests including a complete blood count (CBC), biochemical profile, and urinalysis, although they may be within normal limits.
- Measurement of somatomedin C or insulin-like growth factors (IGF-I) in the blood. With pituitary dwarfism IGF-I levels are decreased due to the growth hormone deficiency.
- Skin biopsy to confirm the presence of a hormonal condition as the source of the skin and hair coat changes
- Measurement of thyroid and adrenal function tests, as other endocrine (hormonal) disorders may also occur
Treatment of Dwarfism in Dogs
Dogs diagnosed with dwarfism are normally treated as outpatients. Treatment includes the following:
- Injections of growth hormone several times weekly for several months
- Thyroid hormone supplementation if thyroid function is abnormal and there is an underproduction of thyroid hormone
- Cortisone replacement if adrenal gland function is severely affected
- Neutering, once affected animals are mature
Administer all medication as directed by your veterinarian. If any change is noted in your dog’s condition, notify your veterinarian.
Hair regrowth is generally noted within one to two months. If hair coat abnormalities recur, GH treatment may be repeated. The dog’s bones usually do not grow substantially on therapy, so the dogs remain short in stature.
There is no known preventative of pituitary dwarfism, but if a puppy is diagnosed with the inherited form of the disease, neither the sire nor dam (father or mother) should be used for breeding again. It would also be advisable to prevent breeding of any of the affected dog’s littermates, for fear that they may be carriers of the disease.