Is Pustular Psoriasis Really Psoriasis?

1. Red Skin and White Scales, Plus Pus?

Small, yellowish pustules appear on the palms or soles. They may burst, form scabs, sometimes be painful, cause fever, and even body aches. Most people say this: "It's a type of psoriasis." But... is that really true? Today, I'll talk about this condition called pustular psoriasis, and its true identity hidden beneath that name.

2. Pustular Psoriasis: Even the Name is Peculiar

This condition is characterized by multiple small pustules, which look like pus, appearing on the entire skin surface or specifically on the palms and soles. It can be generalized, spreading across the body, or localized only to the palms and soles. What's unique is that these pustules are not caused by infection. Neutrophils accumulate in the skin, forming sterile pustules, even without bacteria or viruses. This is pustular psoriasis. But at this point, a question arises: Why is it called psoriasis?

3. The Immune Pathway Itself is Different

In typical plaque psoriasis, keratinocytes abnormally proliferate, the skin becomes red and thick, and is covered with white scales, all via an inflammatory pathway involving IL-23 → IL-17 → TNF-α. However, pustular psoriasis is different. The central pathway is IL-36. Along with this, G-CSF and IL-1β, which attract neutrophils, are also involved. Crucially, some patients have a faulty gene that inhibits the IL-36 receptor. An uncontrolled inflammatory loop. The result? Abnormal immune cell infiltration in the skin → pustule formation. This is actually closer to an autoinflammatory disease than an autoimmune disease.

4. It's Not Just a Different Pathway

Pustular psoriasis progresses more rapidly and is accompanied by systemic symptoms such as elevated body temperature, fatigue, electrolyte imbalance, and even dehydration. In severe cases, it can escalate to an emergency medical condition requiring hospitalization.

5. So Why Do We Still Use the Name 'Psoriasis'?

This is where practical issues arise. There are some histological similarities (e.g., Kogoj's spongiform pustules, inflammatory cell infiltration in the stratum corneum). Some immune pathways, like TNF-α and IL-17A, overlap with common psoriasis. Furthermore, some patients who initially had plaque psoriasis can transition to the pustular form. Moreover, international disease classifications (ICD), insurance systems, and diagnostic tools are still morphology-based. It's convenient to group it under psoriasis if there's redness, scales, and a history of psoriasis.

6. However, Within Academia, the View is Different

Indeed, some researchers argue that pustular psoriasis should be considered an entirely separate disease. There are also opinions to reclassify it as a type of Autoinflammatory Keratinization Disease (AiKD) or Neutrophilic Dermatosis. Especially for patients with IL-36 inhibitory gene defects, known as DITRA syndrome, the pathophysiology and response are entirely different. Naming it psoriasis for these individuals might obscure the true nature of the disease.

7. The Real Problem is That the Name Creates Misunderstandings

Patients might say: "Oh, it's just a type of psoriasis. I'll get better if I moisturize well and apply ointment." But pustular psoriasis is not such a simple disease. It has different responses, a different course, and can sometimes be a life-threatening condition. Because of a single name, diagnosis can be delayed, treatment can go astray, and the prognosis can worsen.

8. Although Still Grouped for Convenience, It May Soon Change

Pustular psoriasis may appear outwardly similar to psoriasis. However, the immune reactions occurring within it are following an entirely different path. In the future, medicine will redefine diseases based on mechanisms rather than appearance, and on immune profiles rather than symptoms. At that time, we may no longer call this condition psoriasis.