In medicine, a disease is considered asymptomatic if a patient is a carrier for a disease or infection but experiences no symptoms. A condition might be asymptomatic if it fails to show the noticeable symptoms with which it is usually associated. Asymptomatic infections are also called subclinical infections. Other diseases (such as mental illnesses) might be considered subclinical if they present some but not all of the symptoms required for a clinical diagnosis. The term clinically silent is also used.
Knowing that a condition is asymptomatic is important because:
It may develop symptoms later and so require watch and wait or early treatment.
It may resolve itself or become benign.
It is required that a person undergoes treatment so it does not cause later medical problems such as high blood pressure and hyperlipidaemia.
Be alert to possible problems: asymptomatic hypothyroidism makes a person vulnerable to Wernicke-Korsakoff syndrome or beri-beri following intravenous glucose.
The affected person may be infectious and unknowingly spread the infection to others.
An example of an asymptomatic disease is Cytomegalovirus (CMV) which is a member of the herpes virus. "It is estimated that 1% of all newborns are infected with CMV, but the majority of infections are asymptomatic." (Knox, 1983; Kumar et al. 1984) In some diseases, the proportion of asymptomatic cases can be important. For example, in multiple sclerosis it is estimated that around 25% of the cases are asymptomatic, being these cases detected postmortem or just by coincidence (as incidental findings) while treating other diseases.
A symptom (from Greek σύμπτωμα, "accident, misfortune, that which befalls", from συμπίπτω, "I befall", from συν- "together, with" and πίπτω, "I fall") is a departure from normal function or feeling which is noticed by a patient, reflecting the presence of an unusual state, or of a disease. A symptom is subjective, observed by the patient, and cannot be measured directly, whereas a sign is objectively observable by others. For example, paresthesia is a symptom (only the person experiencing it can directly observe their own tingling feeling), whereas erythema is a sign (anyone can confirm that the skin is redder than usual). Symptoms and signs are often nonspecific, but often combinations of them are at least suggestive of certain diagnoses, helping to narrow down what may be wrong. In other cases they are specific even to the point of being pathognomonic.
The term is sometimes also applied to physiological states outside the context of disease, as for example when referring to "symptoms of pregnancy". Many people use the term sign and symptom interchangeably.