Priapism

Outline

BASICS

Overview

Persistent erection with engorgement of the CCP, in the absence of sexual arousal
The pudendal nerves control the smooth muscles of the arteries that supply and the veins that drain the CCP
Parasympathetic stimulation of the pudendal nerves causes arterial dilation and venous constriction to/from the CCP to promote erection
- Allows relaxation of the retractor penis muscles (causing penile prolapse) and the smooth muscle cells (allows CCP to fill with blood)
Detumescence is thought to be under sympathetic control
- Agents/conditions interfering with sympathetic stimulation are thought to directly or indirectly block detumescence
- When detumescence fails CO₂ tension in the CCP increases, causing increased blood viscosity and red blood cell sludging and further occlusion of venous outflow from the CCP

Signalment

Predominantly in stallions; geldings can be affected.

Signs

Causes and Risk Factors

Most common—phenothiazine derivatives that block the α-adrenergic impulse to cause detumescence
- Propiopromazine HCl, chlorpromazine HCl, acepromazine maleate
Spinal cord injury or disease
Other causes are rare and include general anesthesia, neoplasia, infectious diseases, postcastration complications, and nematodiasis of the spinal cord

Diagnosis ⬆ ⬇

DIAGNOSIS

Differential Diagnosis

Differentiating Similar Signs

Paraphimosis is the prolapse of the penis and prepuce, with extensive edema of those tissues
Penile paralysis is differentiated by a flaccid prolapsed penis

Treatment ⬆ ⬇

TREATMENT

Massage, hydrotherapy, and application of an emollient dressing to the penis
Elevate the penis in a sling to prevent further complications
Physical replacement in the prepuce under general anesthesia if acute
Flushing the CCP with heparinized saline (10 IU sodium heparin/mL 0.9% saline) using 12 G needles:
- Proximal to the glans penis (ingress) and at the level of the ischium (egress)
- When unresponsive to cholinergic blocking or α-adrenergic agents
Vascular shunt created between the CCP and corpus spongiosum penis—efficacy unknown
Chronic cases with detumescence may need surgery:
- Circumcision (reefing)
- Retraction (Bolz technique) to retain the penis within the prepuce
- Penile amputation

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice

A cholinergic blocker (benztropine mesylate (benzatropine) 8 mg IV slow administration) for acute priapism caused by the administration of α-adrenergic blocking agents (e.g. phenothiazine TQ)
Injection of 10 mg of 1% phenylephrine HCl (an α-adrenergic agent) directly into the CCP during the acute phase if unresponsive to cholinergic blocking agents
Topical or systemic antibiotics for superficial or deep lacerations
Anti-inflammatory medication if secondary paraphimosis or intractable inflammation exists

Contraindications/Possible Interactions

Phenothiazine TQ
Avoid benztropine mesylate and phenylephrine HCl in patients with tachycardia or hypertension

Alternative Drugs

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring

Hospitalization may be needed
Pain and discomfort are managed with physical therapy
Successful reduction of the erection and return of the penis to the prepuce are considered good prognostic indicators

Prevention/Avoidance

Avoid use of phenothiazine TQ.

Possible Complications

Chronic priapism may cause inflammation of the pudendal nerve, causing malfunction of the retractor penis muscles and permanent penile paralysis
Secondary paraphimosis may develop as dependent edema accumulates
Impotence can occur as a result of desensitization of the glans penis (nerve damage) or fibrosis of the CCP (nerve damage)

Expected Course and Prognosis

Prognosis for life is generally good. Return to fertility depends on extent of lesions and complications
Erection and ejaculation can be stimulated by the use of topical testosterone cream and use of a tricyclic antidepressant in stallions with impotence

Miscellaneous ⬆ ⬇

Outline