A 6-year-old boy presented with rash over whole body for a week, and past history of upper respiratory tract infection two weeks ago. Examination revealed extensive guttate erythema with overlying tiny scales; individual lesions measured about 2-10 mm in diameter, and predominantly involved the extremities and trunks (Fig. 1). The rest of the physical examination was normal except tonsillar enlargement. Anti-streptolysin O(ASO) antibody was positive. After receiving the narrowband UVB phototherapy and oral penicillin, the skin lesions gradually faded within 8 weeks, and did not recur over a one-year follow-up.

Fig. 1 Extensive guttate erythematous lesions.

Guttate psoriasis is a subtype of psoriasis characterized by acute eruption of numerous small, erythematous papules and plaques. It usually occurs in children and adolescents, but it can also occur in other age groups. Streptococcus infection is an important risk factor which can usually precedes its development by 2-3 weeks; although, the relationship between streptococcal infection and guttate psoriasis is not fully understood. Although diagnosis is based on clinical, but in the difficult cases, skin biopsy is needed. Differential diagnosis includes pityriasis rosea, tinea corporis, nummular dermatitis and prurigo nodularis. Guttate psoriasis can spontaneously fade within several weeks or several months, phototherapy as a first-line treatment has a good effect, and antibiotics may be used if persisting infection is suspected. Overall, most patients have a good prognosis, just a few patients have a chronic course.