Guttate Psoriasis

Guttate psoriasis is an acute form of psoriasis that presents with many small (2 to 10 mm), drop like, erythematous, scaly papules on the trunk and proximal limbs. It often follows a streptococcal throat infection by 1 to 3 weeks.

It affects mostly children and young adults, and it can be the first manifestation of psoriasis. Roughly one third of patients later develop chronic plaque psoriasis, and the remainder usually clear within 3 to 4 months.

Triggers are throat infection with group A Streptococcus pyogenes (the commonest), perianal streptococcal disease, other infections, stress, skin injury and drugs such as beta blockers, lithium and antimalarials. A family history of psoriasis and carriage of risk alleles raise the likelihood.

Pathophysiology.

Streptococcal antigens that resemble epidermal keratins are thought to activate T cells in genetically susceptible people, with release of interleukin-17, interleukin-23 and tumour necrosis factor. This causes keratinocyte proliferation, neutrophil recruitment and the typical scaly papules.

• Sudden crop of numerous pink red papules with fine silvery scale on the trunk and proximal limbs, sometimes also on the face and scalp.
• Mild to moderate itch, with no systemic upset.
• Palms, soles and nails are usually spared. Nail pitting suggests existing psoriasis.
• Lesions regress over weeks to months, often leaving hypopigmentation or hyperpigmentation.

Red flags.

• Generalised erythema or pustules, suggesting evolution to erythrodermic or pustular psoriasis.
• Fever with sore throat, joint swelling or heart murmur, suggesting rheumatic fever.
• Persisting after 3 to 4 months, or scalp, nail or joint involvement.

• Clinical diagnosis from the distribution and morphology, together with a history of recent sore throat.
• Throat swab for culture, and antistreptolysin O and anti-DNase B antibody titres if infection is suspected.
• Syphilis serology if the palms and soles are involved or the history suggests it.
• Skin biopsy if the diagnosis is unclear: parakeratosis, regular acanthosis, thinned granular layer and neutrophils in the stratum corneum.

Differential diagnosis. Pityriasis rosea, secondary syphilis, pityriasis lichenoides chronica, lichen planus, nummular dermatitis, drug eruption, viral exanthem and tinea corporis.

• Treat a positive throat swab with phenoxymethylpenicillin 500 mg four times daily for 10 days in adults. In children 125 mg four times daily from 1 month to 5 years, 250 mg four times daily from 6 to 11 years, and 500 mg four times daily from 12 years. If penicillin allergic, use clarithromycin 500 mg twice daily for 5 days in adults. Antibiotics do not reliably change the course of the eruption.
• Emollients and mild to moderate topical corticosteroid (clobetasone butyrate 0.05%) once daily for 2 to 4 weeks, with a vitamin D analogue (calcipotriol 50 micrograms/g) once or twice daily on the trunk and limbs.
• Narrowband ultraviolet B two to three times weekly for 6 to 8 weeks is the most effective option for extensive disease.
• Avoid systemic corticosteroids, which can cause rebound into pustular or erythrodermic psoriasis.
• Persistent or recurrent disease: continue under a chronic plaque psoriasis plan, with methotrexate 7.5 to 15 mg once weekly (maximum 25 mg) with folic acid 5 mg weekly, or biologic therapy if severe. Tonsillectomy is considered only for recurrent streptococcal tonsillitis with repeated flares.

Monitoring. Review at 4 to 6 weeks and again at 3 months to detect progression to plaque psoriasis.

Referral and escalation. Refer to dermatology for extensive, severe, persistent or recurrent disease.

Special groups. In children use lower potency steroids and limit the weekly quantity of vitamin D analogue. In pregnancy use topical therapy and narrowband ultraviolet B, and avoid methotrexate.