What are rare diseases?

22 February 2022


IFPA unites all people living with psoriatic disease – regardless of where they live, what type of psoriatic disease they have, or how it impacts their lives. This week, leading up to Rare Disease Day, IFPA is shining a spotlight on rare forms of psoriatic disease.

Join us every day to develop a new topic in rare disease. Together, we will ensure that no one is left behind.

What are rare diseases?

Diseases are classified as rare when they affect only a few people. The threshold for “few” differs from country to country. Generally, diseases are considered rare when they affect fewer than 1 in 2,000 people.

But don’t be fooled! Rare diseases are not rare at all. There are between 5,000 and 8,000 rare diseases in the world. Over 300 million people live with rare diseases every day. In other words, roughly 1 in 25 people has a rare disease. Rare is many.

World Health Organization definition of rare disease

Many countries have unique, prevalence-based definitions of orphan or rare diseases. The World Health Organization defines rare disease as: Serious, chronic or progressive diseases that may be life-threatening and affect a few people in the population.

In epidemiology, prevalence is the total number of cases of a disease in a specific population.

Rare Forms on the Psoriatic Disease Spectrum

Many people are aware of the most common form of psoriasis known as plaque psoriasis or psoriasis vulgaris. This kind of psoriasis is characterized by itchy, flaky patches of skin. However, psoriatic disease is a spectrum, and there are many forms of psoriasis that are rarer and lesser known. Are you aware of the less common forms of psoriatic disease?

About 3% of people living with psoriasis develop pustular psoriasis. This includes Generalized Pustular Psoriasis (GPP) when pustules occur all over the body, and Palmo-Plantar Pustulosis (PPP) when pustules occur on the palms of the hands and soles of the feet. Acrodermatitis continua of Hallopeau (ACH) is an even rarer form of pustular psoriasis that affects the fingers, toes, and nails.

Erythrodermic psoriasis is another severe, life-threatening, and rare form of psoriasis characterized by fiery red skin across the entire body, increased heart rate, severe itching, and change in body temperature.

Finally, arthritis mutilans is a severe, deforming type of psoriatic arthritis that affects less than 5% of people living with PsA. Arthritis mutilans has been associated with pustular psoriasis.

Rare Disease Day is February 28th. IFPA is sharing resources to support people living with rare forms of psoriatic disease as well as their families, friends, and caregivers. Join us in raising awareness of every kind of psoriatic disease on the spectrum.