We report a case of Addison's disease presumed to be secondary to syphilis. The patient
presented with adrenal failure and a maculopapular rash on his trunk and palms. Syphilis
was suspected but the non‐treponemal serological test used (the rapid plasma reagin test
(RPR)) was falsely negative due to the prozone phenomenon. Treatment with benzathine
penicillin resulted in normalization of adrenal function and resolution of the cutaneous
findings. Repeat testing of the previously obtained serum sample showed the RPR to be …