Although a considerable number of patients report penile pain with IC injection therapy, it appears that diabetic men still have high compliance rates with therapy. In one study, 16 of 18 diabetic men continued IC injection therapy for 7 years, compared to 7 of 22 nondiabetic control subjects with ED.57 One possible explanation for this is that diabetic patients with ED have fewer options than do nondiabetic men with ED, who are more likely to have a successful response to oral PDE-5 agents, as documented in one study.58 Another explanation is the greater familiarity with needles and injections among men with diabetes than among their nondiabetic counterparts.
Diabetes doubles or even triples the chance that you’ll have erectile dysfunction (ED) and that you could develop it a decade earlier than other men. In fact, the two conditions are so closely linked that some experts believe that for men younger than 45, impotence, or ED, could be an early warning sign of diabetes. The good news is that diabetes treatment, especially if you identify type 2 diabetes early, can also ease ED.

Cavallini, G., Modenini, F., Vitali, G., & Koverech, A. (2005, November). Acetyl-L-carnitine plus propionyl-L-carnitine improve efficacy of sildenafil in treatment of erectile dysfunction after bilateral nerve-sparing radical retropubic prostatectomy. Urology, 66(5), 1080-5. Retrieved from http://www.sciencedirect.com/science/article/pii/S0090429505006515
Low testosterone levels have been observed inconsistently in STZ-induced diabetic and BB rats.18 Androgen deficiency in rats is associated with downregulation of the neuronal isoforms of nitric oxide synthase, suggesting a trophic effect of testosterone on peripheral erectile tissues. In humans, androgens play a larger role in sexual interest and motivation (libido) than in erectile capacity itself; penile erection is more resistant to androgen withdrawal than is sexual desire.19,20
Diabetes mellitus (DM) is strongly associated with an increased risk of erectile dysfunction (ED), the persistent inability to achieve or maintain an erection sufficient for satisfactory sexual performance, but this condition can be successfully treated in the majority of diabetes patients. ED is present in 32% of type 1 and 46% of type 2 DM patients. Several population- based studies of ED prevalence calculated the odds ratios for the association between ED and various chronic diseases. An odds ratio must be sufficiently greater than 1.0 to identify an increased risk. Diabetes has an odds ratio, ED risk multiplier of 4.1, compared with 1.7 for hyperlipidemia and 1.6 for hypertension. Erectile dysfunction in diabetes mellitus (EDDM) patients has been considered to have an organic etiology. Healthcare providers have long realized that ED can be the first symptom of DM.
If not properly controlled, both type 1 and type 2 diabetes can cause complications due to high blood sugar levels. Over time, these high levels can cause irreversible nerve damage and narrow your blood vessels. While nerve damage may affect the sensitivity of your penis, blood vessel damage can affect the blood flow to your penis and make it more difficult for you to get an erection.
In addition, when research has shown a nutrient such as zinc or niacin to improve sexual function, it's usually in people who are deficient in it. So, before you stock up on over-the-counter nutritional supplements for ED, speak with your doctor. He can test you for deficiencies and steer you toward the most effective and safest way to treat your erectile dysfunction. 
Few simple laboratory tests can help identify obvious causes of organic ED. Initial labs should include HbA1c, free testosterone, thyroid function tests, and prolactin levels. However, patients who do not respond to pharmacological therapy or who may be candidates for surgical treatment may require more in-depth testing, including nocturnal penile tumescence testing, duplex Doppler imaging, somatosensory evoked potentials, or pudendal artery angiography.
Abstract | Full Text | Full Text PDF | PubMed | Scopus (46) | Google ScholarSee all References Sedentary patients with a history of cardiac disease and patients with unstable angina or advanced congestive heart failure should undergo a full medical evaluation before resuming sexual activity.80x80Muller, JE. Triggering of cardiac events by sexual activity: findings from a case-crossover analysis. Am J Cardiol. 2000; 86: 14F–18F
Low intracavernosal nitric oxide synthase levels are found in people with diabetes, smokers, and men with testosterone deficiency. Interference with oxygen delivery or nitric oxide synthesis can prevent intracavernosal blood pressure from rising to a level sufficient to impede emissary vein outflow, leading to an inability to acquire or sustain rigid erection. Examples include decreased blood flow and inadequate intracavernosal oxygen levels when atherosclerosis involves the hypogastric artery or other feeder vessels and conditions, such as diabetes, that are associated with suboptimal nitric oxide synthase activity.
Older age. A man’s risk increases past the age of 40, as age is the variable most strongly associated with impotence. This is due to changing hormones, higher risk for heart problems and those affecting circulation, and decreased sexual desire that often occurs with increasing age. For example, based on findings from the National Health and Social Life Survey, it’s been found that “men between 50–60 years old are more than 3 times as likely to experience erection problems and to report low sexual desire compared to men aged 18 to 29 years.” (3)
Penile arterial supply (top) and venous drainage (middle), longitudinal views. Bottom, Transverse and longitudinal views of venous return. From Lue TF. Physiology of penile erection and pathophysiology of erectile dysfunction and priapism. In: Walsh PC, Retik AB, Vaughan ED Jr, Wein AJ, eds. Campbell's Urology. Vol 2. 7th ed. Philadelphia, Pa: WB Saunders Co; 1998:1157-1179. With permission from Elsevier.

There are no studies specifically assessing the effectiveness of intraurethral suppositories of prostaglandin E1 (PGE-1) in diabetic men. A single randomized clinical trial of the effectiveness of this agent in the general population of men with ED documented that 60% of those who tried this agent were able to achieve successful sexual intercourse.53 Unfortunately, in clinical practice, this agent appears to be considerably less effective.54
Neurological (nerve and brain) diseases: The nervous system plays a vital part in achieving and maintaining an erection. It is common for men with conditions such as stroke, multiple sclerosis (MS), Alzheimer’s disease, Parkinson’s disease, and spinal cord injuries to experience ED. This is due to an interruption in the transmission of nerve impulses between the brain and the penis.
Cardiovascular disease and ED represent 2 common disease processes that are often intimately associated with one another. These common pathophysiological links necessitate a solid scientific and clinical understanding of these 2 disorders and a team effort between the cardiologist and urologist to provide effective management strategies for these patients.
The natural history of ED in people with diabetes is normally gradual and does not occur overnight. Both vascular and neurological mechanisms are most commonly involved in people with diabetes. Atherosclerosis in the penile and pudendal arteries limits the blood flow into the corpus cavernosum. Because of the loss of compliance in the cavernous trabeculae, the venous flow is also lost. This loss of flow results in the inability of the corpora cavernosae to expand and compress the outflow vessels.

Low testosterone represents another link between erectile dysfunction and heart disease. A man’s testosterone levels gradually diminish beginning at age 30. By the time he reaches his 70s, testosterone levels may have dropped to a tenth of youthful levels. Diminishing testosterone levels contribute to loss of muscle, increased body fat, and reduced libido. Fatigue is common, as is depression. Low testosterone levels can also result in reduced concentration, irritability, passivity, loss of interest in activities, and even hypochondria.
Crossref | PubMed | Scopus (23) | Google ScholarSee all References Vardenafil has been shown to be significantly more effective than placebo in the treatment of ED secondary to diabetes mellitus and after radical retropubic prostatectomy.69x69Goldstein, I, Young, JM, Fischer, J, Bangerter, K, Segerson, T, Taylor, T, and Vardenafil Diabetes Study Group. Vardenafil, a new phosphodiesterase type 5 inhibitor, in the treatment of erectile dysfunction in men with diabetes: a multicenter double-blind placebo-controlled fixed-dose study. Diabetes Care. 2003; 26: 777–783
Before a man concludes that oral drugs don’t work for him, he should have his testosterone levels checked to rule out hormone deficiency as the cause of (or as a contributor to) his sexual dysfunction. Other symptoms of low testosterone include a low sex drive and infertility. Checking testosterone levels requires a blood test. If a man’s levels of testosterone are decreased or at the lower end of normal, his doctor may prescribe supplemental testosterone therapy, either as testosterone injections or testosterone gel, which is applied daily to the skin. In some cases, testosterone therapy alone can resolve sexual dysfunction, or it can be combined with the use of oral erectile dysfunction drugs.
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