Page 570 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.2 The male reproductive tr act 545

VetBooks.ir paraphimosis, leading to nerve damage. Other causes PRIAPISM
of reduced retractor penis muscle tone include spinal
disease, myelitis, tumours, severe malnutrition and Definition/overview
exhaustion. Priapism is persistent erection, without sexual
arousal.
Clinical presentation
In complete penile paralysis, the penis is flaccid Aetiology/pathophysiology
and hangs from the preputial cavity. The animal is Priapism occurs due to continued filling/engorge-
unable to retract the penis into the sheath despite ment of the corpus cavernosum with blood.
being touched or exercised. Since lymphatic and Administration of phenothiazine tranquillisers is
venous drainage are disrupted, rapid progression of the most common cause of priapism in stallions and,
the condition ensues, with severe penile swelling, less commonly, geldings. It is thought that the alpha-
skin ulceration and necrosis. In the summer months, adrenergic blocking properties of phenothiazine
fly strike may be a severe problem. tranquillisers block the sympathetic nerve pulses
that initiate penile detumescence. Once blood flow
Differential diagnosis has been disrupted, a cycle of sludging of blood, dis-
Paraphimosis; preputial oedema; trauma. rupted outflow, oedema, thrombosis and eventually
fibrosis occurs. With chronicity, oedema and fibrosis
Diagnosis further disrupt and occlude blood flow. It has been
Manual examination reveals a flaccid penis that is suggested that exposure of colts to mares following
often devoid of sensory sensation. Inability to retract phenothiazine tranquilliser administration increases
the penis during examination is typical. The history the risk of priapism. With prolonged priapism, sec-
and physical examination may provide clues to the ondary conditions such as paraphimosis and penile
underlying cause. paralysis are increasingly likely, due to damage to
the pudendal nerves and retractor penis muscles.
Management Other causes of priapism include tumours, star-
Initial treatment is as indicated for phimosis and vation, debilitation, spinal cord disease and severe
penile and preputial injury, and is aimed at reduc- systemic illness.
tion of swelling and oedema. Placement of the pro-
lapsed, paralysed penis in a sling apparatus will help Clinical presentation
to minimise the gravitational effects on circulation. The animal presents most commonly following
Manual massage may result in sufficient reduction of phenothiazine administration with a firm, partially
swelling so that the penis can be replaced in the pre- erect penis (Fig. 2.150).
putial cavity. Once replaced, the penis may be sup-
ported by a sling or a short-term purse-string suture Differential diagnosis
surrounding the preputial opening. If treatment is The condition must be differentiated from penile
unsuccessful, preputial resection (reefing operation), paralysis and penile trauma.
phallopexy (penile retraction) or partial phallectomy
(penile amputation) is indicated. Diagnosis
A history of phenothiazine tranquilliser administra-
Prognosis tion is typical and physical findings of a persistent
The prognosis for return to full breeding capacity in partial erection are diagnostic. Ultrasound imaging
stallions affected by penile paralysis is poor. Chemical of the penis may demonstrate thrombosis. In the
ejaculation using imipramine (2 mg/kg p/o) followed absence of a history of phenothiazine tranquilliser
1–2 hours later with xylazine (0.66 mg/kg i/v) may administration, a comprehensive work-up, including
be possible. This combination induces ejaculation a neurological examination to rule-out spinal cord
within 20 minutes in approximately 50% of attempts. disease, is warranted.