What does it mean to have a Concomitant Illness?

A concomitant illness is a second illness occurring at the same time as a primary illness. For example, a person with cancer may develop an infection because of a weakened immune system 1. The primary illness can make it difficult to diagnose or treat the concomitant illness, such as when a person with mental illness develops an infection, heart disease, cancer or diabetes and cannot communicate symptoms with his physician or be accountable for treatment.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.

Concomitant Illnesses

Concomitant illnesses may make it more difficult for the treating physician to determine the diagnosis or treatment of the primary illness. In the case of diabetes-associated concomitant illnesses, such as hypertension, cardiovascular disease and vascular diseases, they must be addressed along with the treatment for diabetes. The treatment of these other diseases has an effect on blood sugar levels, so the patient's usual diabetes treatment may have to be changed.


A suppressed immune system can contribute to the development of concomitant illnesses -- patients with HIV/AIDS or cancer may be more vulnerable to infections 1. The treatment of the primary disease may itself cause the concomitant illness, as in liver failure due to high doses of medication over a long period of time. Some concomitant diseases occur together, for instance those with asthma often also have eczema, allergic rhinitis or bronchitis. Other concomitant diseases that are not related to asthma, such as diabetes, heart disease or high blood pressure, can complicate the treatment of asthma.

Clinical Pharmacology

Medications taken for the primary illness and concomitant illness may counteract each other or intensify their effect. Medicines used to treat one illness may have adverse effects on the other illness. Elderly patients being treated for cancer as well as diseases related to aging, such as cardiovascular disease, are vulnerable to dangerous drug interactions.

Treatment of Concomitant Illnesses

A patient with pneumonia complicated by a kidney infection would need a different treatment plan for each illness. A patient who has a throat infection and then develops an ear infection, as well, might be able to be treated with one medication for both problems. Treatment is more effective if the doctor is aware of all the illnesses a patient has, which makes the intake procedure very important. The patient's symptoms may on the surface appear to be caused by the primary illness, but the culprit may be a concomitant illness with similar symptoms. The primary illness may make diagnosing concomitant illnesses difficult, such as when a person with dementia develops diabetes, cardiovascular disease or an infection. Communication between the patient and doctor may be more difficult because of the dementia 1.