What is the difference between “comorbidity” and “multimorbidity”?

Question

I am doing a search on how the number of conditions can cause disease burden. I came across the terms comorbidity and multimorbidty in my search and I wanted to know the difference between the two.

Here are some definitions I found, and I was hoping someone might clear them up for me?

comorbidity – describes medical conditions that exist at the time of diagnosis of the index disease or later, but that are not a consequence of the index disease

multimorbidity – coexistence of several chronic diseases; can be described as existence of two or more chronic diseases.

Answer 1

Comorbidity describes the presence of one or more conditions beside another condition of interest. It can also refer to each of these accompanying conditions. For example:

• Comorbidity (or comorbidities) of x usually include(s) y and z.

• In a study of patients with type 2 diabetes (the main in the study), common comorbidities may include obesity, hypertension, coronary artery disease, among others.

Multimorbidity, refers merely to coexistence of multiple (>=2) conditions, without specifying a main condition of interest. For example:

• A patient with multi-morbidity has the conditions x, y, and z at the same time.

• A patient with coronary artery disease, obesity and hypertension is a patient with multimorbidity. S/he is likely to be on polypharmacy (taking multiple medications for those coexisting conditions).