Pang KH. et al., 2025: Hard-flaccid syndrome: a systematic review of aetiopathophysiology, clinical presentation and management.

Wednesday, 29 October 2025

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Karl H Pang 1 2, Jiarong Feng 3, Yan Zhang 4
1Division of Surgery and Interventional Science, University College London, London, UK.
2Department of Urology, Chelsea and Westminster Hospital NHS Foundation Trust, London, UK.
3Department of Infertility and Sexual Medicine, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China.
4Department of Infertility and Sexual Medicine, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China.

Abstract

Hard-flaccid syndrome (HFS) is a rare condition characterised by a semi-rigid penis in the flaccid state, often accompanied by perineal and urinary symptoms. It may also induce psychological distress, which can exacerbate physical symptoms, creating a vicious cycle. There is currently no standardised treatment for HFS, and management typically focuses on addressing both the underlying causes and presenting symptoms. A systematic review of the literature identified 8 eligible studies. Although the exact aetiopathogenesis remains unclear, it is hypothesised that an initial penile trauma may trigger a cascade of neurovascular and inflammatory events. The associated psychological impact may further perpetuate symptoms, reinforcing the cycle of dysfunction. Common symptoms include perineal pain, urinary disturbances, and erectile and ejaculatory dysfunction. Evaluation involves a comprehensive clinical history, relevant blood and radiological investigations to exclude other pathologies, and the use of symptom questionnaires. Reported treatments include phosphodiesterase-5 inhibitors, anxiolytics, low-intensity shockwave therapy, pelvic floor physical therapy, spinal surgery, and biopsychosocial therapy. Management should be individualised, with a focus on relieving symptoms and breaking the self-perpetuating cycle of HFS. Further evidence-based studies are needed to better understand the pathophysiology of HFS, as well as to develop clear diagnostic criteria and management guidelines.

Int J Impot Res. 2025 Jul 7. doi: 10.1038/s41443-025-01118-2. Epub ahead of print.
PMID: 40624184

Comments 1

Jens Rassweiler on Wednesday, 29 October 2025 10:00

Introduction
Hard-flaccid syndrome (HFS) is a rare condition characterized by a semi-rigid penis in its flaccid state, often accompanied by perineal pain and urinary symptoms. It can lead to significant psychological distress, creating a cycle of physical and emotional suffering. Current treatments are not standardized and focus on symptom management. This study represents a systematic review examined existing literature on HFS, identifying eight eligible studies to summarize its aetiopathogenesis, presentation, and management approaches.

Clinical Presentation
HFS primarily affects men aged 16-42, often following trauma such as aggressive sexual activity or injury. Key symptoms include changes in penis shape, psychological distress, and sexual dysfunction. Diagnosis currently relies on subjective symptom reporting and exclusion of other conditions, with no standardized criteria existing for HFS.

Aetiology and Pathophysiology
Although the precise cause of HFS is not well understood, it is hypothesized to stem from traumatic injury to the neurovasculature, which leads to inflammatory responses and dysregulation of pelvic reflex arcs. This dysfunction may result in increased sympathetic activity, contributing to symptoms such as muscle spasms and chronic pelvic pain. There may also be psychological components, potentially forming a “penis-brain-axis” contributing to symptom prevalence.

Clinical Assessment and Investigations
Evaluation involves blood tests and ultrasound studies to rule out organic causes for erectile issues. Various symptom questionnaires have been utilized to assess severity and impact on quality of life.

Management and Outcomes
Available treatments include phosphodiesterase-5 inhibitors (PDE5i), low-intensity shockwave therapy, physical therapy, and psychological support. Most patients do not achieve complete resolution of symptoms and express dissatisfaction with treatments. Multimodal therapy—addressing both physical and psychological aspects—is recommended but often yields only partial relief.
The role of Li-ESWT in the management of HFS
Low-Intensity Extracorporeal Shockwave Therapy (Li-ESWT) is sometimes utilized in the management of Hard-Flaccid Syndrome (HFS), although its efficacy and role remain areas of ongoing investigation. Here’s a summary of its potential role based on the available literature:

Mechanism of Action: Li-ESWT is believed to promote tissue regeneration, enhance blood flow, and reduce inflammation. These effects can be theoretically beneficial in HFS, where neurovascular dysregulation may contribute to the persistent semi-rigid state of the penis.

Clinical Evidence: While some studies have included Li-ESWT as part of a multimodal treatment approach for managing HFS symptoms, the evidence regarding its efficacy is limited and not robust. The systematic review mentioned that Li-ESWT was used alongside other treatments, such as phosphodiesterase-5 inhibitors and physical therapy, but the outcomes varied significantly among patients. The exact protocols for applying Li-ESWT in HFS can differ, and there is no consensus on the optimal duration, frequency, or intensity of treatment. As Li-ESWT is more commonly used in erectile dysfunction, adaptations for HFS are still under exploration.

Multimodal Approach: In managing HFS, Li-ESWT is often part of a broader therapeutic strategy that may include medications, physical therapy, and psychological support. This multimodal approach recognizes the multifaceted nature of HFS, addressing both physical and psychological components of the syndrome.
Research Gaps: Further studies are needed to delineate the specific effects of Li-ESWT on HFS and to establish standardized treatment protocols. The unique interactions of neurovascular changes, inflammation, and muscle spasms in HFS require targeted research to understand how Li-ESWT can be effectively integrated into treatment plans.

Conclusion
HFS has a complex underlying neurovascular pathophysiology. Management necessitates a tailored, multidisciplinary approach that focuses on symptom relief and the potential need for coping strategies. Further research is warranted to enhance understanding of HFS and establish effective diagnostic and management guidelines. While Li-ESWT offers a potential avenue for symptom relief in HFS due to its regenerative and anti-inflammatory properties, the current understanding of its effectiveness is not definitive. Treatment should be individualized, and further research is essential to clarify the role of Li-ESWT specifically in the management of HFS.

Jens Rassweiler

Clinical Presentation
HFS primarily affects men aged 16-42, often following trauma such as aggressive sexual activity or injury. Key symptoms include changes in penis shape, psychological distress, and sexual dysfunction. Diagnosis currently relies on subjective symptom reporting and exclusion of other conditions, with no standardized criteria existing for HFS.

Aetiology and Pathophysiology
Although the precise cause of HFS is not well understood, it is hypothesized to stem from traumatic injury to the neurovasculature, which leads to inflammatory responses and dysregulation of pelvic reflex arcs. This dysfunction may result in increased sympathetic activity, contributing to symptoms such as muscle spasms and chronic pelvic pain. There may also be psychological components, potentially forming a “penis-brain-axis” contributing to symptom prevalence.

Clinical Assessment and Investigations
Evaluation involves blood tests and ultrasound studies to rule out organic causes for erectile issues. Various symptom questionnaires have been utilized to assess severity and impact on quality of life.

Management and Outcomes
Available treatments include phosphodiesterase-5 inhibitors (PDE5i), low-intensity shockwave therapy, physical therapy, and psychological support. Most patients do not achieve complete resolution of symptoms and express dissatisfaction with treatments. Multimodal therapy—addressing both physical and psychological aspects—is recommended but often yields only partial relief.
The role of Li-ESWT in the management of HFS
Low-Intensity Extracorporeal Shockwave Therapy (Li-ESWT) is sometimes utilized in the management of Hard-Flaccid Syndrome (HFS), although its efficacy and role remain areas of ongoing investigation. Here’s a summary of its potential role based on the available literature:

Mechanism of Action: Li-ESWT is believed to promote tissue regeneration, enhance blood flow, and reduce inflammation. These effects can be theoretically beneficial in HFS, where neurovascular dysregulation may contribute to the persistent semi-rigid state of the penis.

Clinical Evidence: While some studies have included Li-ESWT as part of a multimodal treatment approach for managing HFS symptoms, the evidence regarding its efficacy is limited and not robust. The systematic review mentioned that Li-ESWT was used alongside other treatments, such as phosphodiesterase-5 inhibitors and physical therapy, but the outcomes varied significantly among patients. The exact protocols for applying Li-ESWT in HFS can differ, and there is no consensus on the optimal duration, frequency, or intensity of treatment. As Li-ESWT is more commonly used in erectile dysfunction, adaptations for HFS are still under exploration.

Multimodal Approach: In managing HFS, Li-ESWT is often part of a broader therapeutic strategy that may include medications, physical therapy, and psychological support. This multimodal approach recognizes the multifaceted nature of HFS, addressing both physical and psychological components of the syndrome.
Research Gaps: Further studies are needed to delineate the specific effects of Li-ESWT on HFS and to establish standardized treatment protocols. The unique interactions of neurovascular changes, inflammation, and muscle spasms in HFS require targeted research to understand how Li-ESWT can be effectively integrated into treatment plans.

Conclusion
HFS has a complex underlying neurovascular pathophysiology. Management necessitates a tailored, multidisciplinary approach that focuses on symptom relief and the potential need for coping strategies. Further research is warranted to enhance understanding of HFS and establish effective diagnostic and management guidelines. While Li-ESWT offers a potential avenue for symptom relief in HFS due to its regenerative and anti-inflammatory properties, the current understanding of its effectiveness is not definitive. Treatment should be individualized, and further research is essential to clarify the role of Li-ESWT specifically in the management of HFS.

Jens Rassweiler

Introduction Hard-flaccid syndrome (HFS) is a rare condition characterized by a semi-rigid penis in its flaccid state, often accompanied by perineal pain and urinary symptoms. It can lead to significant psychological distress, creating a cycle of physical and emotional suffering. Current treatments are not standardized and focus on symptom management. This study represents a systematic review examined existing literature on HFS, identifying eight eligible studies to summarize its aetiopathogenesis, presentation, and management approaches. Clinical Presentation HFS primarily affects men aged 16-42, often following trauma such as aggressive sexual activity or injury. Key symptoms include changes in penis shape, psychological distress, and sexual dysfunction. Diagnosis currently relies on subjective symptom reporting and exclusion of other conditions, with no standardized criteria existing for HFS. Aetiology and Pathophysiology Although the precise cause of HFS is not well understood, it is hypothesized to stem from traumatic injury to the neurovasculature, which leads to inflammatory responses and dysregulation of pelvic reflex arcs. This dysfunction may result in increased sympathetic activity, contributing to symptoms such as muscle spasms and chronic pelvic pain. There may also be psychological components, potentially forming a “penis-brain-axis” contributing to symptom prevalence. Clinical Assessment and Investigations Evaluation involves blood tests and ultrasound studies to rule out organic causes for erectile issues. Various symptom questionnaires have been utilized to assess severity and impact on quality of life. Management and Outcomes Available treatments include phosphodiesterase-5 inhibitors (PDE5i), low-intensity shockwave therapy, physical therapy, and psychological support. Most patients do not achieve complete resolution of symptoms and express dissatisfaction with treatments. Multimodal therapy—addressing both physical and psychological aspects—is recommended but often yields only partial relief. The role of Li-ESWT in the management of HFS Low-Intensity Extracorporeal Shockwave Therapy (Li-ESWT) is sometimes utilized in the management of Hard-Flaccid Syndrome (HFS), although its efficacy and role remain areas of ongoing investigation. Here’s a summary of its potential role based on the available literature: Mechanism of Action: Li-ESWT is believed to promote tissue regeneration, enhance blood flow, and reduce inflammation. These effects can be theoretically beneficial in HFS, where neurovascular dysregulation may contribute to the persistent semi-rigid state of the penis. Clinical Evidence: While some studies have included Li-ESWT as part of a multimodal treatment approach for managing HFS symptoms, the evidence regarding its efficacy is limited and not robust. The systematic review mentioned that Li-ESWT was used alongside other treatments, such as phosphodiesterase-5 inhibitors and physical therapy, but the outcomes varied significantly among patients. The exact protocols for applying Li-ESWT in HFS can differ, and there is no consensus on the optimal duration, frequency, or intensity of treatment. As Li-ESWT is more commonly used in erectile dysfunction, adaptations for HFS are still under exploration. Multimodal Approach: In managing HFS, Li-ESWT is often part of a broader therapeutic strategy that may include medications, physical therapy, and psychological support. This multimodal approach recognizes the multifaceted nature of HFS, addressing both physical and psychological components of the syndrome. Research Gaps: Further studies are needed to delineate the specific effects of Li-ESWT on HFS and to establish standardized treatment protocols. The unique interactions of neurovascular changes, inflammation, and muscle spasms in HFS require targeted research to understand how Li-ESWT can be effectively integrated into treatment plans. Conclusion HFS has a complex underlying neurovascular pathophysiology. Management necessitates a tailored, multidisciplinary approach that focuses on symptom relief and the potential need for coping strategies. Further research is warranted to enhance understanding of HFS and establish effective diagnostic and management guidelines. While Li-ESWT offers a potential avenue for symptom relief in HFS due to its regenerative and anti-inflammatory properties, the current understanding of its effectiveness is not definitive. Treatment should be individualized, and further research is essential to clarify the role of Li-ESWT specifically in the management of HFS. Jens Rassweiler

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