Introduction

• Cause: ovarian abnormalities, eg neoplasia, cystic disease.
• Signs: may be non-specific, eg lethargy, weakness, reduced food intake, pale mucous membranes, petechial or ecchymotic hemorrhages on skin and/or mucous membranes, melena, vulval swelling and discharge, bilaterally symmetrical dorsal and/or flank alopecia (this may be the only sign).
• Diagnosis: an appropriate clinical history together with identification of anemia, leukopenia and thrombocytopenia. Additional investigations such as abdominal ultrasonography and elevation in serum estradiol may be indicated in some cases.
• Treatment: supportive care, blood transfusion if anemia and/or thrombocytopenia is significant, remove source of estrogen, prevent recurrence.
• Prognosis: guarded to fair depending on the clinical status of the animal.

Pathogenesis

Etiology

• Persistent seasonal estrus: persistent estrus over one month in duration typically results in hyperestrogenism.
• Other causes:
  • Cystic ovaries Cystic ovarian disease.
  • Estrogen-secreting ovarian remnant.
  • Ovarian neoplasia Neoplasia overview, eg granulosa cell tumors.

Predisposing factors

General

• Entire reproductively active females.

Pathophysiology

• Estrogens (specifically estradiol) is primarily secreted by ovarian follicles in healthy reproductively active mammals, and to a lesser extent in extragonadol tissues such as the kidney, adipose tissue and brain.
• Estrogen under normal physiologic conditions in results in vulval swelling, uterine development, increased sexual receptivity and changes in vaginal cell types.
• Prolonged estrogen exposure (usually accepted as ≥ 1 month) leads to bone marrow suppression and hypoplasia through all blood cell lines:
  • Secondary infection, eg bacterial pneumonia has occasionally been reported.
  • Bleeding diathesis, prolonged clotting times.
• Estrogens, like other androgenic hormones, play a role in the hair cycle and hair follicle structure. Bilaterally symmetrical alopecia is frequently described in animals with androgenic hormonal disorders, although it is difficult to attribute this solely to hyperestrogenism.

Timecourse

• Adverse effects of hyperestrogenism are typically associated with exposure to elevated levels of estrogen ≥ one month.

Epidemiology

• Ovarian cystic disease is a common condition in entire female guinea pigs.
• The published prevalence ranges between 58-100% of the population between 3 months to 5 years of age.
• Serous cysts (cystic rete ovarii) are considered the most common form and are not considered to be steroidogenic.
• Follicular cysts are the second most common type and may induce hyperestrogenism, although there are only few reports published confirming this.

Diagnosis

Treatment

Prevention

Outcomes