Psoriasis is a chronic inflammatory skin disease which is characterized by

  • Increased epidermal proliferation
  • Epidermal thickening
  • Erythematous lesions with silvery white scales

It affects people of all ages in all countries. Its cause remains largely unknown but it has been to variously attributed to genetic, climatic, nutritional, ecological and immunological factors

Triggers of Psoriasis include:

  1. Streptococcal or viral infections
  2. Emotional crises
  3. Pregnancy and delivery
  4. Trauma (Koebner phenomenon)
  5. Diet Alcohol
  6. Cigarette smoking
  7. Hypocalcemia
  8. Stress
  9. Infections e.g. streptococcal pharyngitis

It may occasionally be provoked or exacerbated by drugs including

  1. ACE inhibitors
  2. Calcium channel blockers
  3. P-adrenoceptor antagonists
  4. Lithium
  5. Chloroquine
  6. Non-Steroidal Anti-inflammatory drugs
  7. Terbinafine
  8. Lipid lowering drugs

Symptoms and clinical features of Psoriasis

Lesions are characterized by:

  1. Sharp borders
  2. Erythema
  3. Increased scales: When scratched, scales fall off as tiny flakes that resemble scrapings from a candle (Candle sign). If the scales are removed (exposing the dermal papillae) punctate bleeding from the enlarged capillaries occur (Auspitz sign)
  4. Eruptive lesions may be intensely or mildly pruritic, or may be asymptomatic
  5. All lesions begin as small scaly macules but may take divergent paths as they spread centrifugally
  6. Patterns seen may be:
    • Guttate
    • Follicular
    • Numular
    • Geographic
    • Erythrodermic
    • Annular
    • Gyrate or serpenginous

Favoured sites are:

  1. Knees and elbows
  2. Scalp
  3. Palms and soles
  4. Nails

Intertriginous regions such as the gluteal cleft, groin, penis, labia, axillae, beneath the breasts and between the toes are involved (inverse psoriasis or psoriasis inversa).

There could also be other organ involvement e.g. psoriatic arthritis.

The disease runs a chronic and highly variable course (waxes and wanes)

  1. New lesions may replace older, regressing ones
  2. Unstable lesions may evolve into psoriatic erythroderma or generalized pustular psoriasis
  3. HIV/AIDS can lead to the onset or worsening of psoriasis

Differential diagnoses

Guttate psoriasis:

  1. Pityriasis lichenoides et varioliformis
  2. Acute Pityriasis rosea
  3. Secondary syphilis (psoriasiform syphilis)

Scalp, face, chest lesions:

  1. Seborrhoeic dermatitis
  2. Lupus erythematosus

Chronic truncal psoriasis:

  1. Nummular dermatitis
  2. Lichen planus
  3. Small plaque parapsoriasis

Tinea corporis

  • Pityriasis rubra pilaris

Intertriginous areas:

  1. Candidiasis
  2. Intertrigo
  3. Hailey-Hailey disease


  1. Tinea unguium
  2. Lichen planus
  3. Trachyonychia

Complications of Psoriasis

  1. Erythroderma
  2. Arthritis mutilans


  • Histopathology

Treatment for Psoriasis

Treatment objectives

  1. To retard epidermal proliferation
  2. Reduce inflammation
  3. Prevent complications

Drug treatment

  • Choice of treatment depends on the site, severity and duration of the disease, previous treatment, and the age of the patient

Topical treatment:

Corticosteroid ointment

  • Hydrocortisone for the face and flexures
  • Betamethasone or clobetasol for the scalp, hands and feet

Application is followed by an occlusive
dressing of a polyethylene film, which
may remain in place for 12 – 24 hours to
augment effectiveness.

Dithranol ointment 0.1% -2% (for moderately severe psoriasis)

  • Initiate under medical supervision
  • Start with 0.1%; carefully apply to lesions only, leave in contact for 30 minutes, then wash off thoroughly
  • Repeat application daily, gradually
    increasing strength to 2% and contact time to 60 minutes at weekly intervals
  • Wash hands thoroughly after use
  • Avoid contact with eyes and healthy skin

Coal tar solution (for chronic psoriasis)

  • Use either alone or in combination with exposure to ultraviolet light
  • Apply 14 times daily, preferably starting with a lower strength preparation

Coal tar bath

  • Use 100 mL in bath of tepid water and soak for 10-20 minutes
  • Use once daily, to once every 3 days for at least 10 20 minutes, and for at least 10 baths
  • Often alternated with ultraviolet (UVB) rays, allowing at least 24 hours between exposure and treatment with coal tar

Urea 10% cream or ointment (for dry scaling and itching skin)

  • Apply twice daily, preferably to damp skin

Salicylic acid 3 – 5% in cold cream or
hydrophilic ointment (for thick scaling)

Tazarotene 0.05% and 0.1% gels

  • May be combined with topical steroids for mild-to-moderate plaque psoriasis

Tacrolimus ointment 0.1% or 0.03%

  • For psoriasis in the flexures, face and penis, when potent steroids cannot be used and other agents are poorly tolerated

Small lesions and nail psoriasis

  • Intra-lesional corticosteroid injections of triamcinolone are frequently used
  • Triamcinolone acetonide suspension 10 mg/mL may be diluted with sterile saline to make a concentration of 2.5-5 mg/mL
  • For nail lesions inject triamcinolone in the region of the matrix and the lateral nail fold Scalp
  • Soften scales with salicylic acid 3% in mineral/olive oil, massage in and leave on overnight
  • Then shampoo with a tar shampoo, and remove scales mechanically with a comb and brush
  • Repeat daily until the scales are gone
  • If 3% is not very effective, use 6% salicylic acid


Fluocinolone acetonide 0.01% in oil

  • Apply and leave under a shower cap at night and shampoo in the morning
  • After shampooing and while the hair is still wet, massage thoroughly into the scalp skin
  • Attempting to remove scales by excessive brushing, scrubbing, or combing may result in sufficient trauma worsen psoriasis (Koebner’s effect)

Ultraviolet light (UVL)

  • For psoriasis involving more than 30% of the body surface 290-320 nm ultraviolet B (UVB) three times weekly for 18 – 24 treatments
  • Lubricating the skin surface with mineral oil or petroleum jelly before UVL produces uniform penetration by reducing the reflection of light from the disrupted skin surface

PUVA (psoralen plus ultraviolet A)

  • For patients who have not responded to standard UVB treatment
  • Severe psoriasis unresponsive to outpatient UVL, may be treated in a day care centre with the Goeckerman
  • Use of crude coal tar for many hours and exposure to UVB light

Systemic therapy: Antibiotics to eliminate streptococcal pharyngitis


  • Adult: 20 mg orally once weekly Child: not licensed for this indication
  • Indicated for:
    • Psoriatic erythroderma
    • Moderate-to-severe psoriatic arthritis
    • Acute pustular psoriasis (von Zumbusch type)
    • Involvement of more than 20% total body surface
    • Localized pustular psoriasis that causes functional impairment (e.g. hands)
    • Lack of response to phototherapy, PUVA, or retinoids


  • Induction therapy is 2.5-3.0 mg/kg given in a divided dose twice daily
  • Can be increased to 5.0 mg/kg/day until a clinical response is noted.
  • The dose is then tapered
  • On discontinuation a severe flare-up may occur, suggesting that an alternative treatment (e.g. phototherapy or acitretin) should be instituted as the cyclosporine dose is reduced

Adjuvant therapy

  • Diet: fish oils rich in Q-3 polyunsaturated fatty acids
  • Patient education
  • Emotional support

Notable adverse drug reactions, caution and contraindications

Coal tar:

  • Contraindicated in inflamed, broken or infected skin
  • May cause irritation, photosensitivity reactions, Hypersensitivity
  • Skin, hair, fabrics and bathtubs discoloured brown and smelly


  • Irritant: avoid contact with eyes and healthy skin
  • Contraindicated in hypersensitivity; avoid use on face, acute eruptions, and excessively inflamed areas
  • Discontinue use if excessive erythema occurs or lesions spread
  • Conjunctivitis following contact with eyes
  • Staining of skin, hair, and fabrics brown


  • Avoid application to face or broken skin; avoid contact with eyes
  • May cause transient stinging and local irritation


  • When extensive areas are treated or when there is erythrodermic psoriasis, sufficient may be absorbed to cause adrenal
  • May induce tachyphylaxis
  • Rebound often occurs after stopping treatment, resulting in a more unstable form of psoriasis
  • Intralesional injection may cause reversible atrophy at the injection site

Salicylic acid:

  • Widespread application may lead to salicylate toxicity

Ultraviolet light:

  • Burning of skin may cause Koebner’s phenomenon and an exacerbation
  • Increased risk of skin cancer particularly in persons with fair complexions and albinos.
  • Examine periodically
  • Use protective glasses to prevent cataracts
  • Causes premature ageing of the skin
  • Should be administered only by experienced dermatologists


  • May cause blood disorders (bone
    marrow suppression), liver damage, pulmonary toxicity, GIT disturbances
  • If stomatitis and diarrhoea occur, stop treatment
  • Renal failure, skin reactions, alopecia, osteoporosis, arthralgia, myalgia, ocular irritation, may also occur
  • May precipitate diabetes
  • Monitor before and throughout treatment: blood counts and hepatic and renal function tests
  • Contraception during and for at least 6 months after treatment for both males and females
  • Contraindicated in pregnancy and breast feeding.
  • Folic acid may be given to reduce toxicity


  • Nephrotoxic: monitor kidney function
  • Other side effects
    • hypertrichosis,
    • hyperuricaemia,
    • thrombocytopenia,
    • malignancies and
    • lymphoproliferative
      disorders (similar to other
      immunosuppressive therapies)


See Atopic eczema

Prevention of Psoriasis

  • Avoid exacerbating factors e.g. abrasions, scratches, harsh fibre bathing sponges, and the drugs listed above
  • Prevent streptococcal sore throat and treat promptly when it occurs

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