Pathognomonic symptoms are symptoms that are unique to a particular disease and, as such, establishes a definitive diagnosis.
In the vast majority of cases, symptoms are non-specific to a disease and may be classified as:
- Classic - Highly common for a particular disease and not typically seen in other diseases
- Typical - A symptom seen in most cases of a disease, but not in all cases
- Highly Suggestive - Usually associated with a particular disease, but not unique to that disease.
Pathognomonic symptoms are highly or entirely specific to a particular disease. However, it is not always sensitive, in that some cases may appear without the pathognomonic symptoms.
Although there are single symptoms that are pathognomonic, in most cases there are a small group of symptoms that can establish a definitive diagnosis. Some of the most common are:
- A target shaped rash indicates Lyme disease
- Clustered white lesions next to the 1st and 2nd molars (Koplik's spots) indicate measles
- Rice-watery stool indicates cholera
- Inability to breathe in deeply when the gall bladder is palpitated indicates cholecystitis
- A third heart sound indicates congestive heart failure
- Hydrophobia indicates rabies