Pathognomonic is often used in medicine, that means “characteristic for a particular disease”. A pathognomonic sign is a particular sign whose presence means, beyond any doubt, that a particular disease is present. Pathognomonic is derived from the Greek pathos for “disease” and gnōmon for “indicator”. Labelling a sign or symptom “pathognomonic” represents a marked intensification of a “diagnostic” sign or symptom.

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 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.

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.

Pathognomonic signs of diseases

Table 1. List of pathognomonic signs of different diseases

Duchenne’s Muscular DystrophyGowers’ sign
HypocalcemiaTrousseau sign and Chvostek sign
TetanusRisus sardonicus
Liver cirrhosisSpider angioma
Systemic Lupus ErythematosusButterfly rash
Bulimia NervosaChipmunk facies (parotid gland swelling)
LeprosyLeonine facies (thickened lion-like facial skin)
Cytomegalovirus infectionOwl’s eye appearance of inclusion bodies
Cushing syndromeMoon face
Hodgkin’s lymphomaReed-Sternberg cells (giant mono- and multinucleated cells) upon microscopy
Lyme diseaseErythema chronicum migrans
Inclusion body myositisFilamentous material seen in inclusion bodies under electron microscopy
Tetanus or Strychnine poisoningRisus sardonicus
MeaslesKoplik’s spots
DiphtheriaPseudomembrane on tonsils, pharynx and nasal cavity
Kawasaki DiseaseStrawberry tongue
Grave’s diseaseNew bilateral exophthalmos
EmphysemaBarrel chest
PancreatitisCullen’s sign (bluish discoloration of umbilicus)
Chronic hemorrhagic pancreatitisGrey-Turner’s sign (ecchymosis in flank area)
CholeraRice-watery stool
Typhoid feverRose spots in abdomen
MeningitisKernig’s sign and Brudzinski’s sign
CholecystitisMurphy’s sign (pain on deep inspiration when inflamed gallbladder is palpated)
Angina pectorisLevine’s sign (hand clutching of chest)
Patent ductus arteriosusMachine-like murmur
Parkinson’s diseasePill-rolling tremors
Wilson’s diseaseKayser–Fleischer ring
Whipple’s diseaseOculo-masticatory myorhythmia
Acute myeloid leukemiaAuer rod
Multiple sclerosisBilateral internuclear ophthalmoplegia
PericarditisPericardial friction rub
Rheumatic feverAschoff bodies
RabiesHydrophobia and negri bodies
Acute tubular necrosisMuddy brown casts
Granulosa cell tumorCall-Exner bodies
MalakoplakiaMichaelis–Gutmann bodies
Mammary analogue secretory carcinoma (MASC)ETV6-NTRK3 gene fusion
Narcolepsy (with cataplexy)Cataplexy
Endodermal sinus tumorSchiller–Duval body
Sickle cell diseaseVaso-occlusive crises