Psoriasi guttata

Che cos'è la psoriasi guttata?

Guttate psoriasis is a distinctive acute skin condition characterised by small drop-like, salmon-pink papules which usually have a fine scale. This variant primarily occurs on the trunk and the proximal extremities but it may have a more generalised distribution. A history of an upper respiratory infection secondary to group A beta haemolytic streptococci often precedes the eruption by 2-3 weeks. Guttate psoriasis may be chronic and unrelated to streptococcal infection.

• It is more common in individuals younger than 30 years¹ .

• Genetic predisposition: guttate psoriasis has been linked with HLA-BW17, HLA-B13, HLA-CW6^{2 3} .

• It is most often associated with streptococcal infection - two thirds have evidence of a recent strep throat infection - but may also be associated with stress, trauma (Köbner's phenomenon) or drugs - eg, antimalarials, lithium, non-steroidal anti-inflammatory drugs, beta-blockers⁴ .

• In most cases there is a history of an antecedent streptococcal infection, usually of the upper respiratory tract, such as pharyngitis or tonsillitis, 2-3 weeks prior to the eruption.

• There may be a positive family history of psoriasis.

• The onset of the skin lesions is often acute, with multiple papules erupting on the trunk and the proximal extremities.

• Lesions may sometimes spread to involve the face, the ears and the scalp.

• The palms and the soles are rarely affected.

• The rash is often associated with mild itching.

• Like other forms of psoriasis, guttate psoriasis tends to improve during the summer and worsen during the winter.

• Examination of the skin reveals characteristic lesions consisting of multiple, discrete drop-like salmon-pink papules. A fine scale may be seen on established lesions.
  

  Psoriasi guttata sulle mani

  

  © Mohammad2018, CC BY-SA 4.0, via Wikimedia Commons

• Nail changes characteristic of chronic psoriasis (eg, pits, ridges and the oil-drop sign) are usually absent.

• Nummular dermatitis.

• Pitiriasi rosea.

• Lichen planus.

• Drug eruption.

• Viral exanthem.

• Sifilide.

• Cutaneous T-cell lymphoma.

• Pityriasis lichenoides.

• Diagnosis is clinical and biopsy is usually not required.

• Dermoscopy may be useful in differentiating guttate psoriasis from chronic pityriasis lichenoides⁵ .

• Serology: levels of antibodies to streptolysin O (ASO) may be elevated.

• Cultures: bacterial culture of the throat or perianal area.

Treatment of acute guttate psoriasis is not based on trial evidence; rather, it is guided by expert opinion.

• Usually, the rash resolves within a few weeks to months without treatment for guttate psoriasis, so simple reassurance and emollients may therefore be sufficient.

• Clearance of guttate lesions can be accelerated by judicious exposure to sunlight or by a short course of narrow-band ultraviolet B (UVB) phototherapy, so consider early referral in those who do not respond to topical treatment⁷ .

• Topical treatment with a vitamin D preparation, topical corticosteroid, or coal tar preparation can be considered but may be difficult due to the extent, size and wide distribution of lesions.

• Antibiotic treatment has often been given because of the association between guttate psoriasis and streptococcal infection. However a Cochrane review did not find convincing evidence of benefit and recommended further trials⁸ .

• A prospective study reported that the use of tonsillectomy for patients with chronic guttate psoriasis may be beneficial⁹ .

• Targeted therapy may result from research exploiting the role of the cytokine interleukin (IL)-17 in the pathogenesis of guttate and several other forms of psoriasis¹⁰ .

Complications are largely iatrogenic:

• Steroid-induced cutaneous atrophy, telangiectasia, hypopigmentation.

• PUVA side-effects - eg, nausea and vomiting, photosensitivity.

• Guttate psoriasis often runs a self-limited course over several weeks to a few months with complete remission in about 60%. Other patients go on to develop chronic plaque-type psoriasis. Good prognosis is associated with younger age and high ASO titres, whilst poorer prognosis is associated with a family history of psoriasis¹¹ .

• Scarring is not a problem.

• Previously affected areas may show post-inflammatory hypopigmentation or hyperpigmentation.

• Recurrent episodes may occur, especially with pharyngeal carriage of streptococci.