A Young Male with a Rash of Scales

Mike is 11-years-old and is accompanied by his mother who is very worried about a rash that appeared quite suddenly and has spread over his trunk and his arms. Other than dandruff, he has no history of skin problems. Mike has no other symtpoms, but he is very concerned about the way the rash looks; he says it's "scaly." The slides above offer you a close look at Mike's "scales" and some history. Put the pieces together and, what's your diagnosis? 

References:

Altman K. Guttate psoriasis. Medscape http://emedicine.medscape.com/article/1107850-overview#a1 August 27, 2015.  

Chalmers RJ, O'Sullivan T, Owen CM, Griffiths CE. Interventions for guttate psoriasis. Cochrane Database Syst Rev. 2000;(2):CD001213.

Herbst RA, Hoch O, Kapp A, Weiss J. Guttate psoriasis triggered by perianal streptococcal dermatitis in a four-year-old boy. J Am Acad Dermatol. 2000;42(5 Pt 2):885-887. 

Leung DY, Travers JB, Giorno R. Evidence for a streptococcal superantigen-driven process in acute guttate psoriasis. J Clin Invest. 1995;96:2106-2112.

Menter A, Gottlieb A, Feldman SR, et al. Guidelines of care for the management of psoriasis and psoriatic arthritis: Section 1. Overview of psoriasis and guidelines of care for the treatment of psoriasis with biologics. J Am Acad Dermatol. 2008;58:826-850.

Menter A, Korman NJ, Elmets CA, et al. Guidelines of care for the management of psoriasis and psoriatic arthritis. Section 3. Guidelines of care for the management and treatment of psoriasis with topical therapies. J Am Acad Dermatol. 2009;60:643-659.

U.S. Department of Health and Human Services:  Psoriasis –The Assessment and Management of Psoriasis (2012).  htttp://www.guideline.gov/content.aspx?id=38575&search=guttate+psoriasis. Accessed on August 27, 2015.  

Villeda-Gabriel G, Santamaria-Cogollos LC, Perez-Lorenzo R. Recognition of Streptococcus pyogenes and skin autoantigens in guttate psoriasis. Arch Med Res. 1998; 29:143-148.