Psoriasis
How an immune loop centred on interleukin-23 and interleukin-17 makes keratinocytes multiply about ten times faster than normal, producing thick, red, scaly plaques, and why psoriasis can involve nails, joints and the whole body.
By the end, you can
- Describe normal epidermal turnover and keratinocyte maturation.
- Explain how genetic risk and triggers activate the IL-23/IL-17 axis.
- Explain how accelerated turnover produces thickening, retained nuclei and loss of the granular layer.
- Relate the red, sharply demarcated, silvery-scaled plaque to the underlying changes.
- Describe nail, joint and systemic associations, and distinguish psoriasis from eczema.
- Recognise the classic histology, signs, types and severity scores of psoriasis, and explain how vitamin D analogues, phototherapy, systemic drugs and biologics act on its mechanism.
What it is
Psoriasis is a chronic, immune-mediated inflammatory disease in which keratinocytes proliferate rapidly and mature abnormally, producing well-defined red plaques with silvery scale. It is driven mainly by the IL-23/IL-17 immune pathway, runs in families and is associated with arthritis and cardiometabolic disease.
3 types to tell apart
- Chronic plaque psoriasis
- The commonest form: thick plaques on the elbows, knees, scalp and lower back.
- Guttate psoriasis
- Many small, drop-like plaques, often appearing after a streptococcal throat infection, especially in young people.
- Pustular and erythrodermic psoriasis
- Less common, severe forms with sterile pustules or redness of almost the whole skin.
Normal function
Steady renewal of the epidermis
Keratinocytes divide in the and take about four weeks to travel up through the and to the and be shed.
On the way they mature in an orderly sequence: they fill with keratin, form granules in the granular layer, then lose their nuclei and flatten into the dead, tightly packed cells of the stratum corneum.
Beneath, the rises into the epidermis in small ridges, each carrying a loop of . Immune cells patrol the skin, normally at low levels.
Underlying change · Step 1 of 4
An IL-23/IL-17 immune loop
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 2 of 4
Keratinocytes multiply too fast
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 3 of 4
Red, sharply defined, scaly plaques
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Nails, joints and the whole body
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .