Patients often describe their flaccid penis as firm to the touch, rubbery, shrunken, and retracted, frequently accompanied by pain, discomfort, and various other symptoms.

[1] Among other causes, injuries to the erect penis, blunt trauma to the pelvis or perineum, and damage to the cauda equina are thought to induce this reflex.

The most obvious, unmistakable, and defining symptom of hard flaccid syndrome is a penis that remains in a firm, semi-rigid state in the absence of sexual arousal.

[1][2][3][4][5][6][7] Although not fully understood, the general consensus is that hard flaccid syndrome is caused by elevated sympathetic nervous system activity, or tone, in the penis following a peripheral nerve injury.

In May 2023, Dr. Irwin Goldstein of San Diego Sexual Medicine and colleagues published an article in AUA News presenting a theory on the pathophysiology of hard flaccid syndrome.

[1] The authors identified five potential anatomical sites where this reflex could be triggered: In a June 2024 interview with Stefan Buntrock on the "UroChannel" YouTube channel, Dr. Goldstein discussed region one pathology, stating, “I believe that’s the vast majority of cases,” suggesting that penile injuries are the primary cause of hard flaccid syndrome in most patients.

Patients with region three pathology typically show limited response to treatment, but some have experienced significant improvement or even full recovery following spinal surgery.

[1] In his June 2024 interview with Stefan Buntrock on the "UroChannel" YouTube channel, Dr. Irwin Goldstein discussed the potential link between hard flaccid syndrome and sympathetic axon sprouting.