Signs and symptoms

In medicine, doctors use specific clues to understand an illness, injury, or condition. These clues are categorized into two main types: signs and symptoms. A sign is an objective, observable indication of a medical state. This means a healthcare provider can detect it through physical examination or medical tools. For example, a doctor can see a rash or a bruise on the skin. They can also measure blood pressure or use a stethoscope to listen to internal sounds.

Even a subjective feeling, like feeling hot, becomes a sign once a thermometer provides a specific temperature reading.

A symptom is fundamentally different because it is subjective. It is a personal experience reported by the individual, such as pain, dizziness, or a headache. Symptoms can result from the immune system responding to an infection or the physical effects of a consumed substance. While many symptoms point toward a specific disease, some are idiopathic, meaning they occur without a known cause. Other symptoms are nonspecific, or equivocal, meaning they do not point to one single condition. Common nonspecific symptoms include fatigue, headache, loss of appetite, and malaise. A specific group of these—fever, night sweats, and weight loss occurring over six months—are called B symptoms and are associated with lymphoma.

Medical professionals often look for patterns to narrow down a diagnosis. When a characteristic set of signs and symptoms occurs together, it is called a syndrome. These groups can be categorized by the number of components they contain. A group of three is known as a triad, four is a tetrad, and five is a pentad. For instance, Meltzer's triad is a specific group used to identify cryoglobulinemia. This triad consists of purpura, which is a rash, along with arthralgia (joint pain) and myalgia (muscle pain). Huntington's disease is another example, as it is characterized by a triad of motor, cognitive, and psychiatric signs.

Sometimes, a disease progresses through different stages of visibility. Many illnesses have a prodromal stage, which is an early phase where vague signs appear before specific symptoms emerge. For example, measles has a prodromal presentation involving a cough, fever, and Koplik's spots in the mouth. Over half of all migraine episodes also include a prodromal phase. Conversely, some people are asymptomatic, meaning they have a disease but show no outward signs or symptoms. This can happen with certain cancers or infections like COVID-19. An asymptomatic person may still be able to transmit an infection to others even if they feel healthy.

Symptoms can also be classified by how they change over time. Dynamic symptoms change depending on the circumstances. An example is exercise intolerance, which may appear during physical activity but disappear during rest. In contrast, static symptoms remain fixed and unchanging. Fixed muscle weakness is a static symptom because it does not improve with rest. Some patients with metabolic myopathies experience a "second wind" after six to ten minutes of aerobic exercise, which helps alleviate their dynamic symptoms. This illustrates how the timing and nature of a symptom can provide vital clues about the underlying cause.

Doctors also monitor vital signs to assess overall health status. These are four specific signs that provide an immediate measurement of body function: temperature, heart rate, breathing rate, and blood pressure. The normal ranges for these vital signs vary based on a person's age, weight, gender, and general health. Beyond these, doctors look for cardinal signs or symptoms. These are highly specific indicators that can lead to a certain diagnosis, sometimes even being pathognomonic. In some cases, the total absence of a specific sign, known by the Latin term sine qua non, can be used to rule a condition out entirely.

Finally, the way a body responds to stimuli can reveal neurological issues. A reflex is an automatic response to a stimulus. If a reflex is absent, reduced (hypoactive), or exaggerated (hyperactive), it may indicate damage to the nervous system. For example, the absence of the patellar reflex, known as Westphal's sign, can indicate damage to lower motor neurons. Other specialized observations include the facies, which is a distinctive facial expression associated with certain conditions. Some syndromes may even present with unique facial features, such as elfin facies seen in Williams syndrome.