Answer
Tertiary syphilis is the last/fourth and the most complicated phase of syphilis. Syphilis becomes clinically inactive at the third stage, which is latent syphilis. In some cases the latency does not stay and the infection can proceed to the tertiary stages even after many years of latency. The infection occurring years later would seem unrelated and would not be suspected as syphilis.
Tertiary Syphilis has few/no spirochetes present and this allows it to mimic many other disease making it hard to diagnose.
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