Causes and Pathophysiology:

Three basic mechanisms can lead to erectile dysfunction:

i)Inability to initiate: This could be endocrinologic ,neurogenic ,or psychogenic

ii)Inability to fill: That is arteriogenic

iii)Inability to store adequate blood volume in the lacuna : ie venoocclusive

Vasculogenic Causes:

This will be treated first as it  is the most frequent cause of erectile dysfunction. Here there is a disturbance in the blood flow to and from the penis.

The blood flow to the lacunar spaces in the penis can be decreased in atherosclerosis and traumatic arterial diseases.This results in increased time for full erection and decreased rigidity.

Insufficient relaxation of the trabecular smooth muscle can lead to excessive outflow through the veins even if there is adequate inflow through the arteries.

Endocrinologic Causes:

It is a well established fact that androgens increase libido.

The exact mechanism by which androgens increase libido is not well understood.

Normal testosterone levels are  important ,especially in older males for erectile function.

Erectile dysfunction secondary to hypogonadism can be improved by androgens

Another endocrine cause of impotence is increased level of prolactin .This suppresses gonadotropin-releasing hormone (GnRH), and it also leads to decreased testosterone levels. In these cases normal testosterone and libido can be restored with dopamine agonists, eg bromocriptene .

Diabetes and erectile dysfunction:

35 to 75% of diabetic men suffer from erectile dysfunction. This is mainly due to diabetic vasculopathy or neuropathy.

Diabetics have decreased levels of nitric oxide synthase in the endothelial and neural tissues. Nitric oxide is very important in erection.

Both diabetic microvascular and macrovascular complications can cause erectile dysfunction. Macrovascular complications of diabetes are age related while microvascular complications are related to the duration of diabetes and degree of glycemic control.

Neurogenic Causes:

Damage to the nerves to the penis can result in erectile dysfunction. This can be due to damages/disorders that affect the spinal cord or to the autonomic nerve fibers to the penis.

Spinal cord injury and pelvic surgery can cause erectile dysfunction. Pelvic surgery may disrupt the autonomic nerve supply.

In spinal cord injury, the severity of the erectile dysfunction depends on the level of injury and the completeness of the injury. Injuries to the upper part/incomplete injuries may not lead to erectile dysfunction or may cause mild degrees of erectile dysfunction. Patients with complete injuries or damage to the lower part of the spinal cord usually suffer from erectile dysfunction.

Approximately 75% of patients with spinal cord injury will have some form of erectile capability, but only 25% will have erection sufficient for penetration.

It most be noted that there are many other medical disorders that can affect the spinal cord and /or nerves and lead to erectile dysfunction. Some examples include multiple sclerosis and peripheral neuropathy (eg due to diabetes, alcohol etc).

Psychogenic Causes:

The common psychogenic causes of erectile dysfunction are anxiety, depression, conflicts in relationship, sexual abuse in childhood,loss of attraction, sexual inhibition, conflicts over sexual preference, fear of sexually transmitted diseases and fear of pregnancy.

Even patients with organic causes of erectile dysfunction develop a psychogenic component as a reaction to the erectile dysfunction.

References:

Pages 272 to 274,Chapter 43. Sexual dysfunction. Part II Cardinal Manifestations and Presentation of Diseases. Harrison’s Principles of Internal Medicine, 16th Edition by Kasper, Braunwald, Fauci, Hauser, Longo and Jameson. Volume I. Mc Graw Hill publication.

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