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790.e2 Pituitary Dwarfism

Pituitary Dwarfism
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• Pituitary dwarfism is also connected to
BASIC INFORMATION
decreased glomerular filtration. Lack of TREATMENT
Definition GH and thyroid hormones may result in Treatment Overview
Rare clinical syndrome of congenital growth maldevelopment of the glomeruli. • Supplementation of GH is often not neces-
hormone (GH) deficiency • Atlanto-axial malformation may lead to sary. Porcine GH is not always available and
instability and dynamic compression of the can be expensive, and progestins have many
Synonym cervical spinal cord. side effects. Therapy with progestins can
Congenital hyposomatotropism • Cystic enlargement of Rathke’s cleft was be considered if response to therapy with
previously thought to be the cause of CPHD; thyroxine is inadequate.
Epidemiology it is now recognized as the result. • If GH deficiency is treated, the goal is to
SPECIES, AGE, SEX normalize serum IGF-1 concentration. Close
• Rare in dogs, more so in cats DIAGNOSIS monitoring for adverse effects caused by the
• Signs usually apparent at 2-5 months of age treatment is needed (see Possible Complica-
• No sex predisposition Diagnostic Overview tions below).
Definitive diagnosis should rely on genetic • Therapy for hypothyroidism is required for
GENETICS, BREED PREDISPOSITION testing or endocrine function tests. cases of CPHD.
Encountered most often in German shepherd
dogs, Czechoslovakian wolfhounds, and Saar- Differential Diagnosis Chronic Treatment
loos wolfhounds as an autosomal recessive, The differential diagnosis is discussed on p. 946. • Canine GH is not available.
inherited disorder • Antibodies directed against human and
Initial Database bovine GH preclude their use.
ASSOCIATED DISORDERS • CBC, biochemistry profile, and urinalysis help • Porcine GH does not result in antibody
• Previously mentioned dog breeds have a rule out other causes of growth retardation. formation.
combined pituitary hormone deficiency • Creatinine concentration is elevated in most ○ Starting dose of 0.1-0.3 IU/kg SQ q
(CPHD) of GH, thyroid-stimulating dwarfs. 48-72h (3 times/week)
hormone (TSH), and prolactin together with ○ Dose should be adjusted based on the
an impaired release of gonadotropins but not Advanced or Confirmatory Testing serum IGF-1 concentration. The goal is
adrenocorticotropic hormone (ACTH). • Basal serum GH concentrations can be low to maintain IGF-1 concentrations in the
• Dwarfs may have atlanto-axial malformation in healthy animals. Definitive diagnosis of reference range; however, reference ranges
and instability. CPHD is based on a stimulation test. vary, depending on the laboratory and
○ GH-releasing hormone (GHRH) 1 mcg/ size and age of the dog. Monitoring can
Clinical Presentation kg IV or alpha-adrenergic drugs, such be difficult.
HISTORY, CHIEF COMPLAINT as clonidine 10 mcg/kg IV or xylazine ○ Increase in body size depends on the
• Growth retardation 0.1 mg/kg IV, can be used. status of the growth plates at the time
• Retention of puppy haircoat ○ GH concentrations are determined GH treatment is initiated. A beneficial
• Alopecia immediately before and 20-30 minutes response of the skin and haircoat usually
• Persistent estrus after IV administration of the stimulant. occurs within 6-8 weeks of the start of
• Dwarfs with atlanto-axial instability may ○ In healthy dogs, plasma GH concentra- therapy.
display progressive weakness, ataxia, and tions should increase at least twofold to • Progestagens can be used as an alternative
star gazing. fourfold. There is no significant rise in because they stimulate mammary GH
plasma GH concentration in pituitary production in dogs; the GH is released into
PHYSICAL EXAM FINDINGS dwarfs. the systemic circulation.
• Proportionate dwarfism ○ Xylazine and clonidine may cause seda- ○ Medroxyprogesterone acetate (MPA)
• Bilaterally symmetrical alopecia affect- tion, bradycardia, hypotension, and 2.5-5 mg/kg SQ q 3 weeks for 5 doses,
ing points of wear, sparing the head and vomiting. then q 6 weeks improves clinical signs in
extremities ○ GH levels should be determined by a affected dogs.
• Abnormally soft, wooly haircoat species-specific, homologous radioim- ○ Proligestone 10 mg/kg SQ q 3 weeks has
• Hyperpigmentation and scaling of exposed munoassay. Availability of GH assays is been reported to be similarly effective.
skin limited. • Dogs with CPHD should be treated with
• Pyoderma • An indirect assessment of GH can be achieved levo-thyroxine (p. 525).
• Unilateral or bilateral cryptorchidism by measuring the serum insulin-like growth
• Dwarfs with atlanto-axial instability may factor 1 (IGF-1) concentration. There may be Possible Complications
show ataxia, paraparesis or tetraparesis, some overlap in concentration with healthy • Progressive chronic kidney disease
hypermetria, and opisthotonus. dogs. • Pyoderma
• Dwarfs should be screened for hypothyroid- • Atlanto-axial joint instability
Etiology and Pathophysiology ism as part of CPHD. • GH therapy: acromegaly and diabetes mel-
• CPHD is characterized by underdevelop- • Imaging (radiographs, CT, MRI) of the litus (DM)
ment of the pituitary gland and deficiency atlanto-axial joint may reveal abnormal • Progestagen treatment: pyoderma, skel-
of GH, TSH, prolactin, and gonadotropins; positioning of the dens axis and incomplete etal maldevelopment, mammary tumors,
ACTH secretion is unaffected. Mutations ossification of the suture lines between the acromegaly, DM, and cystic endometrial
of the LHX3 gene, which is a regulator of ossification centers of the atlas. hyperplasia. In bitches, ovariohysterectomy
pituitary development, are associated with • Genetic testing can be used to identify dwarfs should be performed before the start of
this form of pituitary dwarfism. and carriers with the LHX3 mutation. progestagen treatment.

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