Pathognomonic (synonym pathognomic) is a term, often used in medicine, that means "characteristic for a particular disease". A pathognomonic sign is a particular sign whose presence means that a particular disease is present beyond any doubt. The absence of a pathognomonic sign does not rule out the disease. Labelling a sign or symptom "pathognomonic" represents a marked intensification of a "diagnostic" sign or symptom.
The word is an adjective of Greek origin derived from πάθος pathos 'disease' and γνώμων gnomon 'indicator' (from γιγνώσκω gignosko 'I know, I recognize').
Practical use
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. 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. The presence of a pathognomonic finding allows immediate diagnosis, since there are no other conditions in the differential diagnosis.
Singular pathognomonic signs are relatively uncommon. Examples of pathognomonic findings include Koplik's spots inside the mouth in measles, the palmar xanthomata seen on the hands of people suffering from hyperlipoproteinemia, Negri bodies within brain tissue infected with rabies, or a tetrad of rash, arthralgia, abdominal pain and kidney disease in a child with Henoch–Schönlein purpura, or succinylacetone for Tyrosinemia Type I.
As opposed to symptoms (reported subjectively by the patient and not measured) and signs (observed by the physician at the bedside on physical exam, without need for a report) a larger number of medical test results are pathognomonic. An example is the hypersegmented neutrophil, which is seen only in megaloblastic anemias (not a single disease, but a set of closely related disease states). More often a test result is "pathognomonic" only because there has been a consensus to define the disease state in terms of the test result (such as diabetes mellitus being defined in terms of chronic fasting blood glucose levels).
In contrast, a test with very high sensitivity rarely misses a condition, so a negative result should be reassuring (the disease tested for is absent). A sign or symptom with very high sensitivity is often termed sine qua non. An example of such test is a genetic test to find an underlying mutation in certain types of hereditary colon cancer.
Examples Disease Sign Cytomegalovirus infection Owl's eye appearance of inclusion bodiesPage 268 in: Lyme disease Erythema chronicum migrans Inclusion body myositis Filamentous material seen in inclusion bodies under electron microscopy Hypocalcemia Trousseau sign and Chvostek sign Tetanus or strychnine poisoning Risus sardonicus Measles Koplik's spots Wilson's disease Kayser–Fleischer ring Diphtheria Pseudomembrane on tonsils, pharynx and nasal cavity Chronic hemorrhagic pancreatitis Grey-Turner's sign (ecchymosis in flank area) Cholera Rice-watery stool Enteric fever Rose spots in abdomen Meningitis Kernig's sign and Brudzinski's sign Angina pectoris Levine's sign (hand clutching of chest) Patent ductus arteriosus Machine-like murmur Parkinson's disease Pill-rolling tremors Whipple's disease Oculo-masticatory myorhythmia Acute myeloid leukemia Auer rod Multiple sclerosis Bilateral internuclear ophthalmoplegia Pericarditis Pericardial friction rub Rheumatic fever Aschoff bodies Rabies Hydrophobia and Negri bodies Gout Tophi Acute tubular necrosis Muddy brown castsGranulosa cell tumourCall-Exner bodiesMalakoplakiaMichaelis–Gutmann bodiesNarcolepsy (with cataplexy)CataplexyEndodermal sinus tumorSchiller–Duval bodyParkinson's diseaseRigidity with tremorAtrial flutterFlutter wavesSickle cell diseaseVaso-occlusive crisesLightning injuryLichtenberg figure on skin
See also AIDS-defining clinical condition List of eponymous medical signs Medical sign
References
External links
Slide show with audio summary of 122 pathognomonic signs