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In medical terms a [sign] is an objective, observable, measurable expression of a pathology. To a physician, the combination of a patient's clinical and familial history (anamnesis), combined with the patient's symptoms and signs allows for a proper diagnosis. Some signs are so subtle and specific that they can only be observed and understood by a trained health care professional. Furthermore, some signs are pathognomonic, that is, by their presence they define a pathology. Furthermore
Contrary to symptoms (which are subjective), signs are not only objective, but comparable between individuals of the same species. Therefore we can compare the heart rate bmp (beats per minute) between normal and sick individuals allowing us to chart a range from normal to abnormal. The same is true for most signs such as body temperature, respiratory capacity, breathing rate, weight, height, etc.
Some signs are particular to a pathology, although they may not be pathognomonic. These specific signs are usually eponymic, such as:
• McMurray's sign: A click caused by the meniscus during manipulation of the knee; indicative of meniscal injury.
• Blumberg's sign: Sharp piercing pain on the abrupt release of steady pressure over the site of a suspected abdominal lesion, indicative of peritonitis. When used to diagnose appendicitis over McBurney's point it may be called Aaron's sign.
• Musset's sign: Rhythmical jerking of the head following the heart pulsations in aortic aneurysm and aortic insufficiency.
• Cardarelli's sign: An abnormal pulsation of the trachea that may be found in patients with an aneurysm of the aortic arch that causes left tracheal displacement.
• Caput medusae: A ring of dilated varicose veins radiating from the umbilicus, usually indicative of portal hypertension.
• Papal Benediction Sign: A contraction of the fourth and fifth digits, as in benediction (see image).
There are many more medical signs, this list is only an illustration of the concept