A sore right shoulder can really be a message from the gallbladder
Medicine draws a sharp line between what you feel and what a doctor can observe. A headache is a symptom; a high thermometer reading is a sign. The two often overlap, sometimes mislead, as when gallbladder inflammation shows up as shoulder pain, and occasionally vanish entirely while a disease quietly spreads.
A sign is objective: a rash, a bruise, clubbed fingernails, an odd gait, a blood pressure reading or a shadow on a scan. A symptom is a personal report, such as pain, dizziness or feeling feverish. They can meet in the middle, since a patient's sense of fever becomes a sign once a thermometer confirms it. The word symptom comes from Greek for something that befalls you, and Henry Stubbe described the study of these clues as semiotics in 1670, long before the term was borrowed for the study of communication.
Some clues are far more telling than others. Nonspecific complaints like fatigue, night sweats and weight loss fit countless conditions. A pathognomonic sign points to one condition alone. Clusters help too: three linked findings form a triad, and Meltzer's triad of rash, aching joints and weak muscles suggests cryoglobulinemia. Absence can be just as useful, because a missing essential feature, the sine qua non, can rule a diagnosis out. When a child's features suggest a genetic disorder that testing cannot identify, doctors may use the label syndrome without a name.
Timing matters. Many illnesses start with a prodrome, early hints before the full picture appears; measles, for example, opens with cough, fever and Koplik's spots in the mouth, and more than half of migraine episodes have such a phase. Conditions may go quiet in remission and flare again in relapse. Some symptoms are dynamic, as in McArdle's disease, where exercise intolerance eases after six to ten minutes in a so-called second wind, while fixed weakness is static.
Reflexes and faces carry information as well. A missing knee jerk, known as Westphal's sign, can indicate damage to lower motor neurons, while an exaggerated one hints at upper motor neuron trouble. Four vital signs, temperature, heart rate, breathing rate and blood pressure, give an instant snapshot of overall health. And some diseases, including certain cancers and infections, produce no signs or symptoms at all yet can still be passed on or found by accident on a scan.
Source: Signs and symptoms
