International Psoriasis Council

Advancing Knowledge. Improving Care.

Advancing Knowledge. Improving Care.

Why a New Psoriasis Disease Severity Classification System Will Better Serve Psoriasis Patients

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Over 20 years ago, the criteria for psoriasis disease severity were created. To be considered a severe form of the disease, a patient had to meet a minimum PASI or BSA score of 10%.

In two decades, these criteria have remained largely unchanged.

Meanwhile, knowledge about psoriasis — including drug safety, comorbidities, and impacts on a patient’s physical and mental health — has increased exponentially. We now know the risks of leaving psoriasis, even seemingly minor cases, untreated. We also have treatment options to safely and effectively treat patients with varying levels of the disease.

Unfortunately, due to a rigid and dated disease severity classification system, the opportunities to improve patient quality of life are limited. The current classification system has lagged significantly behind recent knowledge about psoriasis, and it’s time for a change.

The proposal: A new criteria for severe psoriasis

International Psoriasis Councils’ Psoriasis Severity Reclassification Project aims to change the classification of psoriasis severity. IPC’s network of key opinion leaders agreed on a definition for each category of disease severity. 


IPC’s disease severity reclassification project seeks to challenge using the standard definitions of “mild, moderate, and severe” to determine treatment pathways. Through a robust Delphi process, IPC’s network of experts developed a consensus statement that redefines the criteria for patients who are candidates for systemic therapy. The statement is as follows:

Patients that meet one or more of the following criteria are candidates for systemic therapy:

Moving forward, the focus will shift to implementing studies that quantify the statement in real-world practice. In addition, there will be an emphasis on educating clinicians and patients on the new classification, including educating regulatory bodies and developing additional activities to educate clinicians and patients.

An evolution of psoriasis knowledge and drug safety

At the time of the classification system’s origination, existing knowledge about psoriasis was much more limited than today.

Systemic medications were believed to potentially be toxic to patients or carry significant risks. There was also a belief that psoriasis was not that bad — and would not warrant treatment with a potentially risky systemic medication. The current classification system was designed to lead to other drugs of choice, such as topical and light therapies, which were generally believed to be safe.

Since the system’s creation, safer systemic drugs have been developed. There is also an increased understanding of the profound impacts of psoriasis on a patient’s overall health.

The classification criteria were also intended to reserve new systemic psoriasis medications for patients who had what was considered severe psoriasis. Now, we know that psoriasis can carry significant risks — arthritis, heart disease, diabetes, and psychosocial problems, to name a few. We also know that untreated psoriasis can significantly shorten a patient’s lifespan by up to 5 years.

Despite these advances surrounding the disease and drug safety improvements, the criteria for receiving systemic therapy have not changed since they were set two decades ago.

The impacts of a dated classification system

The current clinical definitions of psoriasis severity are narrowly defined. They overlook the unique challenges faced by each patient, such as localized lesions in specific areas and/or comorbidities.

With the current classification system, patients are unnecessarily denied entry to clinical trials and declined reimbursements for treatments. Clinicians are also limited in what treatment options they have available to their patients.

The way we classify psoriasis disease severity must change. A more specific clinical severity classification would guide clinical decision-making to be more practical, meaningful, and better aligned with the true severity of a patient’s disease. This would strengthen psoriasis treatment guidelines, and it would also guide future clinical trials of drugs targeting various severities of psoriasis.

How new disease severity criteria will better serve psoriasis patients

The past two decades have been a time of great improvement in psoriasis knowledge and drug safety. However, without a new set of criteria for disease severity, clinicians are limited in providing safe systemic medications that can greatly improve their patients’ physical health and quality of life.

New criteria would change this. It would allow clinicians to reach patients who have widespread psoriasis (greater than 10% BSA or PASI), and more patients who would benefit from these treatments but don’t fall into this strict qualification.

In particular, two groups of patients who experience severely impacted quality of life — but may not be considered severe under the current classification system — include patients who have:

  • Psoriasis localized to areas of their bodies, like the face, palms, soles, or genitalia
  • Failed topical therapy

Additionally, the amount of psoriasis on someone’s skin is not the whole story of psoriasis severity. The main comorbidity of psoriasis — psoriatic arthritis — can occur when there are very small or even no amounts of skin psoriasis. In these cases, psoriasis severity should consider the presence and impact of comorbidities, especially when making treatment decisions about these patients.

Treating psoriasis that is less widespread may limit the spread of psoriasis in the future. What’s more, if treated earlier in life, it could also reduce the impact of the disease later in life, such as the development of arthritis or heart disease.

Embracing a much needed change in psoriasis disease severity classification

The psoriasis disease severity classification drives much of psoriasis treatment. From clinical trial acceptance to patient reimbursement to treatment options, the severity of a patient’s psoriasis currently depends on what is too rigid of a standard.

The past two decades have led to crucial research and improvements in psoriasis treatment and medication, and the current classification system doesn’t reflect this. The disease severity classification system is due for a change to utilize, in each individual patient, the most effective treatment to address the needs of that individual.


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