Neurologic conditions are causal factors in about 10% to 20% of ED cases. Various diseases and disorders may affect the brain's sex centers or other parts of the nervous system such as the hypothalamus, pituitary gland, spinal cord, and peripheral nerves supplying the penis, all of which play important roles in sexual development and function. Brain lesions, for example, may disturb the secretion of vital neurotransmitters, such as dopamine and oxytocin, and inhibit the transmission of neural impulses from the sex centers to the penile nerves via the spinal cord. Causes of such lesions include stroke, Alzheimer's disease, tumor, epilepsy, CVA, infection, parkinsonism, multiple sclerosis (MS), and trauma.
Spinal cord lesions caused by conditions such as injury, tumors, infections, MS, diabetic neuropathy, herniated disk, and neurosyphilis may be associated with loss of psychogenic and possibly reflexogenic erections as well as absence of sexual pleasure, orgasm, and ejaculation. These problems are due to disturbed transmission of sensory impulses from the penis to the brain and motor stimuli from the brain to the penis. The severity of the dysfunction depends on the level and extent of the lesion, particularly in relation to the secondary sex center in the sacral spine. Any pathology involving the sacral sex center leads to the absence of both reflexogenic and psychogenic erections. Trauma to the pelvic or penile nerves, by disrupting passage of neural impulses to and from the penis, can cause sensation loss and ED.
In cases of spinal cord injury, it has been reported that about 70% of paraplegics or quadriplegics are sexually active and that about 70% of them practice alternate forms of sexual expression such as oral or genital stimulation. One study found that reflexogenic erections were present in about 95% of patients with spinal injuries above the sacral vertebrae, and that psychogenic erections were maintained in about 25% of patients with partial sacral injuries. Although erectile ability was preserved in about 90% of those patients with incomplete lesions, those erections were generally unpredictable and brief, with poor ejaculation, precluding normal sexual functioning.