To better understand the potential causes of priapism, it is useful to understand how erections occur.
Erections
When a man becomes sexually aroused, his nervous system releases a chemical called nitric oxide. Nitric oxide relaxes and widens the walls of the arteries that supply blood to the penis. This increases the flow of blood into the spongy tissue of the penis, causing it to expand and harden into an erection.
Once the feelings of sexual arousal have passed, the arteries in the penis should get smaller, pushing the excess blood out of the penis and returning it to its normal floppy state.
Therefore, anything that affects either the nervous system or blood flow (or both) can trigger the symptoms of priapism.
Common causes
The most common causes of priapism are discussed below.
Sickle cell anaemia
Sickle cell anaemia is a genetic (inherited) blood disorder where red blood cells develop abnormally. Red blood cells carry oxygen from the lungs to the rest of the body. The cells are usually round and flexible, allowing them to move easily around the body.
However, in people with sickle cell anaemia, the shape and texture of red blood cells can change. They become hard and sticky and are shaped like sickles (crescents). Occasionally, the hardened blood cells can become trapped in the blood vessels of the penis, leading to the symptoms of ischaemic priapism.
See the Health A-Z topic about sickle cell anaemia for more information about the condition.
Medications
A number of medications can occasionally disrupt the normal workings of the nerves that are responsible for helping to trigger an erection by widening the arteries in the penis. The nerves essentially ‘forget’ to narrow the arteries after the feelings of sexual arousal have passed. This leads to the symptoms of ischaemic priapism.
Types of medication that have been associated with ischaemic priapism include:
- oral medications (tablets or capsules) that are used to treat erectile dysfunction, such as sildenafil (Viagra), tadalafil (Cialis) or vardenafil (Levitra)
- medications for erectile dysfunction, which are injected directly into the penis, such as alprostadil
- blood-thinning medication, such as warfarin or heparin
- some types of antidepressants, such as fluoxetine (Prozac) and bupropion
- some medications that are used to treat high blood pressure (hypertension), such as calcium channel blockers
In addition, some recreational drugs have been linked to priapism. They include:
- cocaine
- ecstasy
- methamphetamine (crystal meth)
- cannabis
Less common causes
Less common causes of priapism include:
- thalassaemia – a blood condition that is similar to sickle cell anaemia
- cancers of the blood, such as chronic leukaemia and multiple myeloma
- cancers that have spread from nearby tissue or organs, such as prostate cancer or bladder cancer, and are disrupting the blood flow inside the penis
- spinal cord injury
- blood clots
- Fabry disease – a rare, genetic condition that affects the metabolism (the process that converts food into energy)
