A symptom (from Greek σύμπτωμα, "accident, misfortune, that which befalls", from συμπίπτω, "I befall", from συν- "together, with" + πίπτω, "I fall") is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality. A symptom is subjective, observed by the patient, and not measured.
Symptoms may be chronic, relapsing or remitting. They also may progressively worsen or progressively become better. Conditions may also be classified as symptomatic (present and demonstrating symptoms) or asymptomatic (present but without symptoms). Asymptomatic conditions and asymptomatic infections can exist for many years undiagnosed and may only be found upon medical testing (such as high blood pressure).
Constitutional or general symptoms are those that are related to the systemic effects of a disease (e.g., fever, malaise, anorexia, weight loss). They affect the entire body rather than a specific organ or location.
The terms "chief complaint", "presenting symptom", or "presenting complaint" are used to describe the initial concern which brings a patient to a doctor. The symptom that ultimately leads to a diagnosis is called a "cardinal symptom".
Some symptoms occur in a wide range of disease processes, whereas other symptoms are fairly specific for a narrow range of illnesses. For example, a sudden loss of sight in one eye has a significantly smaller number of possible causes than nausea does.
Some symptoms can be misleading to the patient or the medical practitioner caring for them. For example, inflammation of the gallbladder often gives rise to pain in the right shoulder, which may understandably lead the patient to attribute the pain to a non-abdominal cause such as muscle strain.
Symptom versus sign
A symptom can more simply be defined as any feature which is noticed by the patient. A sign is noticed by other people. It is not necessarily the nature of the sign or symptom which defines it, but who observes it.
A feature might be sign or a symptom, or both, depending on the observer(s). For example, a skin rash may be noticed by either a healthcare professional as a sign, or by the patient as a symptom. When it is noticed by both, then the feature is both a sign and a symptom.
Some features, such as pain, can only be symptoms, because they cannot be directly observed by other people. Other features can only be signs, such as a blood cell count measured in a medical laboratory.
A constitutional symptom is a symptom that affects the general well-being or general status of a patient. Examples include weight loss, shaking, chills, fever, malaise and vomiting. It might be an indication that a disease or disorder is affecting the whole body. 
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