Singular pathognomonic signs are relatively uncommon.
The presence of a pathognomonic finding allows immediate diagnosis, since there are no other conditions in the differential diagnosis. A pathognomonic sign or symptom has very high positive predictive value and high specificity but does not need to have high sensitivity: for example it can sometimes be absent in a certain disease, since the term only implies that, when it is present, the doctor instantly knows the patient's illness. While some findings may be classic, typical or highly suggestive in a certain condition, they may not occur uniquely in this condition and therefore may not directly imply a specific diagnosis. The word is an adjective of Greek origin derived from πάθος pathos 'disease' and γνώμων gnomon 'indicator' (from γιγνώσκω gignosko 'I know, I recognize').
Labelling a sign or symptom 'pathognomonic' represents a marked intensification of a 'diagnostic' sign or symptom. A pathognomonic sign is a particular sign whose presence means that a particular disease is present beyond any doubt. Pathognomonic (rare synonym pathognomic ) is a term, often used in medicine, that means 'characteristic for a particular disease'. Medical term meaning 'characteristic for a particular disease'
