What Is a “Phenotype”?
A phenotype is a “type” or “pattern” of a disease.
- It is based on what symptoms you have
- It can include test results, like what doctors see during a scope of the bladder
- It can include pain in other parts of the body and other health problems you may have
Knowing your IC/BPS phenotype can help:
- You and your doctor pick better treatments
- Set more realistic goals
- Decide which specialists might help (for example, pelvic floor physical therapy, pain management, mental health support)
The 2 Main IC/BPS Phenotypes
Experts at a 2025 global meeting on IC/BPS agreed that two main phenotypes are most important right now:
Pain that is centered around the bladder and the surrounding area. This phenotype includes patients with Hunner lesions and/or low anesthetic bladder capacity (i.e., under anesthesia, the bladder can only be filled with up to 400 or 500 cc of liquid).
These types are mostly centered in the bladder itself. People often have stronger bladder symptoms and fewer whole‑body symptoms.
Hunner Lesion (HL) Type
- What it is:
- A Hunner lesion is a sore on the bladder wall
- Doctors see it during a bladder scope (cystoscopy)
- Under the microscope, there is clear inflammation in the bladder lining
- Who tends to have this type:
- Often older adults, as symptoms may start later in life (often after 40-50 years)
- People with strong bladder and urinary symptoms
- Treatments that often help this type:
- Treating the lesion directly, for example:
- Burning or cauterizing the lesion (fulguration)
- Injecting steroid medicine into the lesion
- Sometimes, immune‑calming medicine (like cyclosporine A)
- Other bladder treatments (like bladder Botox) can help too
Even if the lesion heals after treatment, the person is still considered to have the Hunner lesion phenotype.
Low Bladder Capacity Type
Another bladder‑centered type is based on how much the bladder can hold when you are asleep under anesthesia.
- What it is:
- Doctors fill the bladder during surgery while you are asleep
- They measure how much your bladder can safely hold
- If the bladder holds less than a certain amount, this is called low anesthetic bladder capacity
- Features of this type:
- People with low-capacity bladders are often similar to those with HL:
- Older, and develop symptoms later in life
- Have stronger bladder symptoms
- Have fewer other chronic pain conditions
- Under the microscope, the bladder lining also looks inflamed
- Many people with Hunner lesions also have low bladder capacity. Because of this, experts think:
- Hunner lesion type and low capacity type are closely related
- Both may be part of a broader “bladder‑centric” group
Widespread pain throughout the body that is not exclusive to the bladder area. Patients in this phenotype often have other, related conditions (i.e., co-morbid conditions), such as endometriosis, fibromyalgia, and irritable bowel syndrome.
Some people with IC/BPS have pain that is not just in the bladder or pelvis. It can be found in many parts of the body. People with this phenotype are thought to have a condition called “central sensitization,” in which signals in the central nervous system lead the brain to perceive pain more intensely.
- What it is:
- Pain in several body areas
- Many people have pain in three or more regions outside the pelvis
- This is often called “widespread pain”
- Other common features:
- People with widespread pain often:
- Are younger
- Have less severe bladder symptoms
- Have more “chronic overlapping pain conditions” (COPCs) such as:
- Irritable bowel syndrome (IBS)
- Fibromyalgia
- Migraine
- Chronic fatigue
- Have more problems with:
- Sleep
- Fatigue
- Memory or concentration (“brain fog”)
- Have higher rates of:
- Anxiety
- Depression
- Post‑traumatic stress disorder (PTSD)
Many have faced traumatic life events, including sexual violence. More trauma often goes along with more widespread pain.
- Why this type matters for treatment:
- People with widespread pain may respond better to nervous‑system‑focused medicines, such as certain antidepressants used for pain (for example, amitriptyline)
- Bladder‑only treatments may help less if the main problem is whole‑body pain processing
- These patients may benefit from a team approach, including:
- Pain management
- Mental health support
- Sleep and stress care
- Gentle physical activity programs
Doctors may use simple body pain maps to see if your pain is widespread, which helps place you in this phenotype.
You can have more than one of these at the same time.
It is also important to note that people in either of the above phenotypes can have what is called myofascial pelvic pain. This involves tight, painful, or “spasm‑like” muscles in the pelvis and can be determined by a gentle pelvic exam. Pelvic floor muscle problems are very common in IC/BPS, and people with significant myofascial pelvic pain often do not respond as well to basic bladder treatments alone.
Variable Phenotypes?
It’s important to note that not everyone with IC/BPS will fit neatly into one of the two phenotypes described above. Other emerging potential phenotypes are also being explored by researchers. These include recurrent urinary tract infections (that occur alongside IC/BPS), but it is important to note that current science does not support embedded infection or differences in the microbiome as underlying causes of the condition.
