although marked

[Mher]

Hi, friends. What does the author mean by saying "although marked"?
"The advances of the malady are, luckily, gradual. The first manifestations, although marked, are unequivocal. The fits grow successively more and more distinctive, and endure each for a longer term than the preceding."

 

[probus]

In this context "marked" means "highly noticeable". On the other hand "unequivocal" means "permitting only one interpretation or meaning". I am at a loss to understand why the author chose to treat "marked" and "unequivocal" as opposites. It is probably a question of professional jargon. We have doctors among our teachers ...