Pseudopregnancy, or hysterical pregnancy, or pseudocyesis is a clinical condition characterized by behavioural and physiological changes that occur in non-pregnant female dogs during diestrus. In cats, pseudopregnancy corresponds to the period of activated corpora lutea in the absence of pregnancy (approximately 35 days) and only rarely is it accompanied by physical and behavioural changes. Pseudopregnancy, typical of the final stage of diestrus (from week 6 to week 12 after the end of oestrus) affects 50-70% of dogs, regardless of breed or size, and can already occur after the first heat.
Pseudopregnancy consists of variable clinical symptoms typical of pregnancy, such as: increased appetite, weight gain and abdominal distension; the most striking symptom is hyperplasia of the mammary gland and sometimes galactorrhoea. The behavioural changes are typical of a dog about to give birth: restlessness or decreased physical activity, dysorexia/anorexia, hyperemesis and maternal attitudes (searching for and preparing the "nest", an attempt to suckle inanimate objects) (Fig. 1). This process is particularly important in packs of wild canids. In fact, the simultaneous presence of subjects with lactogenesis at the end of the heat periods makes it possible for unmated females (usually of lower rank within the pack) to suckle the pups of the dominant females in case of need, such as the mother's death.
AETIOPATHOGENESIS
The precise mechanism involved in the development of clinical pseudocyesis is still unknown, although some researchers believe that clinical symptoms are an exaggeration of the physiological processes characteristic of diestrus. Particular emphasis is given to the decrease in the progesterone level in the blood and the resultant increase in prolactinaemia. The sharp decrease in concentrations of progesterone after luteolysis, around the eighth week in cases of pregnancy, or between the sixth and twelfth week, or after ovariectomy during diestrus, results in an increased secretion of prolactin, a hormone that primarily serves to control milk secretion and the onset of the maternal instinct. As these hormonal changes occur in all female dogs, pregnant or not, it is not easy to understand why the symptoms of pseudopregnancy are not found in all non-pregnant dogs.
Several studies have been conducted to measure levels of prolactinaemia in dogs, with or without clinical signs of pseudopregnancy, but, although some of these studies have shown higher levels of prolactin in symptomatic patients, most researchers found no difference between dogs with or without pseudopregnancy. It is possible that other hormones, in correlation with prolactin, may play an important role in the onset and maintenance of this process.
Some studies have shown a possible link between environmental factors and the onset of pseudopregnancy in female dogs. Among these, the type of diet would seem to influence the onset and/or development of the symptoms, even if the endocrine mechanism has not yet been identified. The hypothesis of a breed predisposition, related to a different duration of the luteal phase, has not been confirmed. These considerations suggest that the clinical symptoms of pseudocyesis depend on an excessive production of prolactin or a particular individual sensitivity to prolactin.
SYMPTOMS AND DIAGNOSIS
Pseudopregnancy is characterized by symptoms similar to those of imminent whelping, with a considerable individual variation in the severity of symptoms. The dog may be more restless and less inclined to physical activity; there is often the presence of dysorexia or anorexia and, occasionally, vomiting, diarrhoea, polyuria, polydipsia and polyphagia. The dog frequently tends to retire to isolated places, as though she was preparing the "nest", and shows maternal attitudes towards inanimate objects. The owners are often led to believe that there is really an imminent birth because there may be abdominal contractions and an actual lactation with galactorrhea.
Lactation is usually driven by self-stimulation or suckling by other subjects; potential complications, such as mastitis or mammary dermatitis, are not common. The symptoms of pseudopregnancy usually disappear after 2-4 weeks. Some particularly susceptible female dogs have a high incidence of recurrence in subsequent heats, often with a worsening of the symptoms. To rule out a pregnancy in progress, the diagnosis is based on the medical history, abdominal palpation, ultrasound and radiographic exams. In the case of anorexia, vomiting, polydipsia and depression, a differential diagnosis must be made to rule out the diseases typical of canine diestrus (pyometra). In women, some systemic diseases, such as hypothyroidism have been associated with high levels of prolactinaemia and consequent galactopoiesis, but there are no detailed studies on such conditions in the dog.
TREATMENT AND PROGNOSIS
In 95% of cases, treatment is not necessary because normally the clinical signs tend to decrease spontaneously within 2-4 weeks. In fact, the degree of mammary distension, through a neuroendocrine reflex (baroreceptors), induces a reduction in the secretion of prolactin. However, in dogs who present with a state of malaise, mainly secondary to the increased size of the mammary gland and to galactorrhea, local packs can be applied, alternately hot and cold, to try to reduce the size of mammary glands. This, however, much like the milking of the mamma, may lead to persistent lactation due to the continuous stimulation of lactogenesis. It may be helpful to use an Elizabethan collar to prevent lapping and self-suckling by the dog. Similarly, it can be useful to associate a behavioural therapy, by removing the inanimate objects and attempting to distract the dog by encouraging her to do exercise. A diet low in fat and protein may sometimes be useful, as well as the removal of water for 5-7 nights.
In the past, in some cases, mild sedation was resorted to with tranquillizers, even repeated for several days, with drugs not based on phenothiazines because of their antagonistic action against prolactin-inhibiting substances. In the past, steroid hormones were always administered, particularly progestogenic hormones (megestrol acetate, 2 mg/kg/day for 8 days), to restore the typical diestral state. However, there was the risk of relapse at the time of withdrawal of treatment and possible complications, such as: pyometra/cystic endometrial hyperplasia, mammary tumours and insulin resistance. Other hormones used were androgens (testosterone and mibelerone) or oestrogenic compounds, all with varying results and serious side effects.
Currently, the prescribed drug therapy is usually based on antiprolactinic compounds that can antagonise prolactin. The secretion of prolactin by the pituitary gland is under the inhibitory control of the hypothalamus, which acts through the direct action of dopamine or the indirect action of serotonin. These drugs are used mainly to prevent the stagnation of milk and the consequent onset of inflammatory processes (mastitis) in the mammary gland, which may lead to possible general after-effects. The most commonly used antiprolactins are cabergoline, having direct action on the dopamine receptors, and metergoline, a serotonin antagonist with dopaminergic effects at high doses. Cabergoline is used at a dose of 5 µg/kg live weight orally for 4-6 days, with the possibility of repeating the treatment in case of relapse. The reported side effects consist in episodes of vomiting within 1-2 hours after administration of the drug and a slight loss of appetite during the treatment. Metergoline (0.2 mg/kg live weight orally for 8-10 days) should be used with caution in subjects who are particularly aggressive or anxious because, due to its central antiserotoninergic action, it can cause anxiety, aggressiveness and hyperexcitability.
The prognosis of pseudopregnancy, which is simply an exacerbation of a physiological event, is certainly favourable. Complications are mainly related to the onset of mastitis; in fact no correlations with the onset of sterility or other genital diseases have been observed, while doubts remain about the hypothesis of it possibly being a risk factor for the onset of benign mammary cancer. In case of repeated episodes of a certain severity, sterilization through ovariectomy after remission of the clinical symptoms may be advisable, in order to make it easier for the owners to manage the situation.
Suggested readings
- SD Johnston, MV, R Kustritz, PNS Olson. Canine and Feline Theriogenology. Saunders edition, 2001.
- Gobello G, De La Sota RL, Goya RG. A review of canine pseudocyesis. Reproduction in Domestic Animals, 2001; 36:283-288
- Burke TJ. Small Animal Reproduction and Infertility. A Clinical Approach to Diagnosis and Treatment. Lea & Fabiger, Philadelphia, 1986.