Nodular mucinosis misdiagnosed as non-responsive secondary syphilis

A previously healthy 24-year-old man presented with an erythematous, non-pruritic and painless papulonodular skin rash affecting the trunk, upper arms (excluding palms), neck, face, forehead and scalp. He had a penile ulcer for the past 2 weeks, almost healed at the time of observation. The patient tested positive for syphilis and HIV-1; he claimed being negative for HIV 6 months earlier. As the palms were not affected, we performed a skin biopsy for the differential diagnosis between secondary lues and acute HIV seroconversion reaction. Benzathine penicillin (2,400,000 units) was administrated and antiretroviral therapy started. Although the skin biopsy was compatible with secondary syphilis, there was no change in the skin rash 3 weeks after the first penicillin administration. Another 2 doses of penicillin were given but 4 weeks later the rash persisted. A second biopsy revealed a mucinous skin infiltration, compatible with nodular mucinosis.