Chapter 4: Papulosquamous Disorders
Psoriasis
What is it?
Psoriasis is an inflammatory disorder that causes thick, red, and scaly plaques to appear on the skin. The tendency to get psoriasis is passed in families, but there is usually a trigger such as an infection that causes it to appear for the first time. Psoriasis is more common in adults. In the pediatric population, the prevalence increases with age, being highest in teenagers. Rarely psoriasis can start at birth or in the infancy period.
There are many systemic disorders linked to psoriasis, including arthritis, obesity, and metabolic syndrome. Psoriasis has a major impact on quality of life.
What does it look like?
The distribution of the psoriatic plaques is often symmetrical and distributed on the elbows, knees, lower back, and scalp. The plaques are erythematous to salmon in colour with a sharp demarcation. The scales in psoriasis are very thick and can become silver in colour (Micaceous scale). More than 50% of patients have pruritus but not as severe as in atopic dermatitis.
Scalp plaques are thick and can lead to tinea amiantacea, a term used when hairs clump with thick scale. The hair line is a common site of involvement. The external auditory canal and post auricular skin are often involved. An important site to examine in patients with psoriasis are the nails. This helps support the diagnosis. Nail involvement can be the solo presentation.
| Nail Sign | Description |
| Pitting | Small circular depressions on the nail plate |
| Onycholysis | Separation of the nail plate from the nail bed |
| Oil drop sign | Yellow orange discolouration under the nail plate |
| Subungual hyperkeratosis | Thickness under the distal nail |
Koebner Phenomena
Development of psoriasis on areas of trauma, indicates that the condition is active. This also can be a feature of other cutaneous disorders like lichen planus, vitiligo and warts.
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Subtypes of psoriasis:
- Psoriasis vulgaris or chronic plaque psoriasis- see above
- Guttate psoriasis: numerous raindrop-like psoriasis papules and plaques, often follows a streptococcal infection such as pharyngitis or perianal strep. Treatment includes both antibiotics and psoriasis therapies. Phototherapy is a good option if available.
- Pustular psoriasis: a widespread pustular eruption with background of erythema. Can be widespread and associated with constitutional symptoms. The use of systemic corticosteroid in patients with psoriasis vulgaris or arthritis that can lead to a pustular psoriasis flare when the steroid is discontinued. Treatment with acitretin is often recommended.
- Erythrodermic psoriasis: with wide-spread erythema > 80-90% body surface area and associated exfoliation. This can be the first presentation of psoriasis, clues to the diagnosis can be family history or nail involvement. Skin biopsy may be necessary
What causes psoriasis?
Psoriasis is a cutaneous disorder with an immune dysregulation. The high rate of epidermal proliferation triggered by the immune system causes to the thick plaques and associated scale. An increase in Th1 and Th17 cells leads to the inflammatory reaction and increased cytokines seen in psoriasis. These have been a target for new biologic therapies, which have shown great success in adult patients with psoriasis and psoriatic arthritis
What makes it worse?
In pediatric psoriasis, associated streptococcal infection of the throat or perianal skin should be evaluated. Other triggers include medications like NSAIDs, beta blockers, antimalarial, interferons and lithium. Ironically, tumour necrosis alpha inhibitors are used to treat psoriasis but can lead to a paradoxical psoriasis reaction, involving the palms, soles and scalp, when used to treat inflammatory bowel disease.
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How is it treated?
Treatment depends on how much of the skin is involved, what areas of skin are involved, and how thick the plaques are. Prednisone is avoided, because of the risk of developing pustular psoriasis when it is withdrawn.
Topical Therapies
- Mid-high potency corticosteroids like mometasone and clobetasol.
- Topical vitamin D derivatives (calcipotriene) ointment alone or in combination with betamethasone dipropionate.
- Betamethasone diproprionate with salicylic acid- for thick scales, the salicylic acid helps exfoliate the scale.
Face and genital region
Topical tacrolimus or pimecrolimus are very effective. Avoid using potent topical corticosteroids, because of risk of atrophy and striae formation.
Scalp involvement
Fluocinolone acetonide oil for mild scalp involvement to help life the scales. Betamethasone membrane or Clobetasol scalp lotion for thicker areas.
Phototherapy
When available, narrow band UVB (NBUVB) is the mode most often used. It is helpful for widespread involvement especially with thin plaques. Other options include broad band UVB, UVA/UVB and Psoralen plus UVA (PUVA). Treatments are given 2-3 times a week for a duration of at least 3 months.
Systemic Therapy
Moderate to severe involvement >10% body surface area may require systemic treatments in combination with the above therapies. Common systemic agents used in psoriasis are methotrexate, cyclosporin, acitretin (vitamin A derivative) and biological therapies. The targeted biologic therapies including inhibitors of TNF alpha and IL 12/23 inhibitors. These are best directed under the care of a dermatologist when possible.
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| Atopic Dermatitis | Psoriasis | |
| Incidence | Very common | Less common |
| Family history | Family history of atopy | Family history of psoriasis |
| Flexors vs extensor | Involves flexors (except infantile) | Extensors |
| Pruritis | Pruritus (must) | Pruritus very common >50% |
| Secondary infections | Higher risk of secondary infections | Less infections |
| Nail involvement | Nails are involved less often | Specific nail findings |
| Koebner phenomena | - | + |
| Joint involvement | - | +/- psoriatic arthritis |
