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Erectile dysfunction: Causes (Etiology)

• Erectile Dysfunction: Epidemiology and causes
• Erectile Dysfunction: Signs, symptoms and diagnostic workup
• Erectile Dysfunction: Medical and surgical treatment

Review literature: (Lue, 2000) (Porst, 2004).

Definition of Erectile Dysfunction

Erectile dysfunction (ED) is the inadequacy of erection for at least 6 months duration, which prevents a satisfactory sexual intercourse in more than 70%.

Synonyms: impotentia coeundi.

Epidemiology of Erectile Dysfunction

Prevalence:

A rising prevalence of erectile dysfunction with age can be shown. In the Massachusetts male aging study (MMAS) the prevalence rate of ED was 8% (40–49 years), 16% (50–59 years) and 37% (60–69 years) (Johannes et al., 2000).

In Germany, a pronounced age dependency is also observed. But, despite the rising prevalence with age, there is a high sexual activity in each age group (96–71%). The prevalence of erectile dysfunction is 2% (30–39 LJ), 10% (40–49 LJ), 16% (50–59 LJ), 34% (60–69 LJ), 53% (70–79 LJ). Overall, the prevalence was 19%, but only 7% were dissatisfied with their sexuality and wanted a treatment (Braun et al., 2000).

Epidemiological Risk Factors for Erectile Dysfunction

Many life stye factors and diseases influence the prevalence of erectile dysfunction (in brackets the relative risk according to Johannes et al (MMAS), 2000):

Diabetes mellitus (RR 1.8):

Diabetes mellitus is the most important risk factor for erectile dysfunction. Diabetes mellitus leads to macroangiopathy, microangiopathy and neuropathy: multifactorial reasons for erectile dysfunction.

Cardiac diseases (RR 1.5–1.9):

Coronary artery disease untreated (1,5), coronary artery disease under medication (1.9), arterial hypertension with medication (1,5). Conversely, erectile dysfunction is a clinical sign and risk factor for (yet unrecognized) peripheral or coronary artery disease.

Smoking (RR 1.2):

Smoking leads to vasoconstriction and smooth muscle contraction, in the long run smoking promotes arteriosclerosis. In the MMAS-Study, smoking contributes only in smaller parts to the prevalence of erectile dysfunction, whereas in other studies the impact is greater.

Alcohol:

Chronic abuse of alcohol harbours the risk of marital problems, hypogonadism and polyneuropathy, all risk factors for erectile dysfunction.

Protective factors:

The MMAS-study identified a high educational status (0.64) and high income (0.73) as protective factors against erectile dysfunction.

Etiology (Causes) of Erectile Dysfunction

Psychogenic Causes of Erectile Dysfunction:

Depression, anxiety disorders, psychotic disorders and psychiatric medication for treatment of these disorders can cause or aggravate ED (20–50%). Various psychological conditions (anxiety, overwork, education, depression, trauma or decreased self-esteem) lead to sympathetic overactivity during intercourse and thus to erectile dysfunction. The mental fixation on erectile dysfunction with above mentioned psychological patterns can also arise on the basis of an organic ED. Half of men under 40 years with ED have an exclusively psychogenic cause.

Neurogenic Causes of Erectile Dysfunction

Diseases of the CNS:

CNS lesions disrupt the activation of spinal erection centers and cause erectile dysfunction. Important brain centers for the erectile function are: limbic system, hypothalamus (paraventricular nucleus and medial area praeoptica) and thalamus. Lesions of these brain areas can be triggered by a variety of disorders: cerebral hemorrhages or ischemic stroke, Alzheimer disease, Parkinson disease, tumors or multiple sclerosis.

Spinal diseases:

The vast majority of young men after spinal cord injury suffer from erectile dysfunction. Erectile dysfunction is typical for caudal (lumbar) injuries, because injury to the sacral erection center is more likely. Reflexogenic erections with good rigidity may be present cervical or thoracal injury.

Peripheral nerve lesions:

Diabetes mellitus, vitamin deficiency, alcoholism, pelvic surgery (radical prostatectomy, cystectomy, rectum resection, pelvic fractures). The injury of the cavernous nerves lead to degenerative processes and apoptosis of the erectile tissue with shrinking of the penis.

Hormonal Causes of Erectile Dysfunction

Diabetes mellitus:

Diabetes mellitus damages the peripheral nerves (diabetic neuropathies) and arteries (diabetic angiopathy), causing a multifactorial erectile dysfunction.

Hypogonadism or PADAM:

Androgen deficiency supresses sexual interest and nocturnal erections. The standard value of testosterone for older men and the indication for hormone replacement therapy to treat erectile dysfunction are uncertain. Low concentrations of DHEA correlate better than low concentrations of testosterone with the prevalence of erectile dysfunction.

Hyperprolactinemia:

Medication and pituitary tumors are the most common causes for hyperprolactinemia. Hyperprolactinemia causes a hypogonadotropic hypogonadism which leads to infertility, gynecomastia and erectile dysfunction.

Hyperthyroidism or hypothyroidism:

Thyroid disorders are rarely the cause of erectile dysfunction, the likelihood of hypothyroidism as a cause of erectile dysfunction is 4%.

Cushing Syndrome:

Hypercortisolism affects the gonadal hormone axis in 70%.

Vascular Factors Causing Erectile Dysfunction

Arterial diseases:

A reduced arterial inflow leads to reduced venous compression and thus to an insufficient erection (reduced rigidity or premature detumescence). The most common cause for a decreased arterial supply is a peripheral arterial disease (PAD) associated with the usual risk factors (smoking, hypertension, diabetes mellitus, lipid metabolism disorders). Other causes of arterial insufficiency are trauma or pelvic radiation therapy. Conversely, erectile dysfunction is a clinical sign and risk factor for (yet unrecognized) peripheral or coronary artery disease.

Venous diseases

Please refer to the next section: Cavernosal and Veno-occlusive Disorders.

Cavernosal and Veno-occlusive Disorders

Many diseases of the corpora cavernosa or veins lead to a veno-occlusive disorder with insufficient venous compression and insufficient reduction of venous outflow. The increased venous outflow leads to erectile dysfunction.

• Congenital oversized veins
• Impaired relaxation of the cavernous smooth muscle: fibrosis, degeneration, dysfunction of the GAP-junctions. Non-penile erectile dysfunction (e.g., nerve injury) causes in the course of the disease a fibrosis and degeneration of the erectile tissue, which complicates treatment. The reason for the increased fibrosis seems to be inadequate oxygenation. Intermittent erections are necessary for adequate oxygenation of the erectile tissue and are prophylactic against fibrosis.
• Diseases affecting the tunica albuginea: Peyronie disease, trauma.
• Shunt between corpora cavernosa and corpus spongiosum: after surgery for priapism, congenital, after trauma.
• Inadequate neurotransmitter release due to endothel dysfunction.

BPH and Erectile Dysfunction

Benign prostatic hyperplasia with severe symptoms of obstruction is a risk factor for ED.

Medication-Induced Erectile Dysfunction

• Antihypertensive therapy: thiazides, spironolactone, beta-blocker.
• Antiandrogens: cyproterone acetate, flutamide, bicalutamide, GnRH agonists, GnRH antagonists, ketoconazole, 5-alpha-reductase inhibitor.
• Sedative or anticholinergic effect: antidepressants, sedatives, neuroleptics, hypnotics, antiepileptic drugs.
• Various effects: cimetidine (hyperprolactinemia).

Aging and Systemic Diseases

Following factors become more prevalent with age and may cause erectile dysfunction:

• Reduction of smooth muscle cells
• altered extracellular matrix
• decrease in NO production
• increased α1-receptor density
• decrease of free testosterone (PADAM) or DHEA
• decrease of growth hormone
• increased life time with risk factors causing erectile dysfunction: diabetes mellitus, arterial hypertension, lipid disorders, impact of tobacco use.
• Increased prevalence of chronic diseases: chronic kidney disease, dialysis, myocardial infarction, pulmonary emphysema, liver cirrhosis...

References

Johannes u.a. 2000 JOHANNES, C. B. ; ARAUJO, A. B. ; FELDMAN, H. A. ; DERBY, C. A. ; KLEINMAN, K. P. ; MCKINLAY, J. B.: Incidence of erectile dysfunction in men 40 to 69 years old: longitudinal results from the Massachusetts male aging study.
In: J Urol
163 (2000), Nr. 2, S. 460–3

Lue 2000 LUE, T. F.: Erectile dysfunction.
In: N Engl J Med
342 (2000), Nr. 24, S. 1802–13

Porst 2004 PORST, H.: Tadalafil, Therapiestrategien bei erektiler Dysfunktion.
Linkenheim-Hochstetten : Aesopus Verlag, 2004

  Deutsche Version: Erektile Dysfunktion