Jim Flaherty, Canada's former finance minister who died of an apparent heart attack on Thursday at age 64, suffered from a rare skin disease called bullous pemphigoid.

The politician revealed in January 2013 that he had the disease, which affected his appearance the past couple of years. It is unknown whether there is any connection between his condition and what a close family friend described as a massive heart attack.

Bullous pemphigoid is an autoimmune disease in which the person's immune system produces antibodies against the skin. It is not infectious.

When the antibodies attack, the skin separates. It usually starts with a red, itchy rash that resembles eczema or hives.

Itchy blisters can then appear that tend to last weeks or months. Mouth sores and bleeding gums are other symptoms.

It is usually diagnosed by blood tests and skin lesion biopsies.

Corticosteroids such as prednisone may be prescribed. Flaherty was prescribed prednisone to help with the condition.

If used in large doses for prolonged periods of time, the side-effects of prednisone can include indigestion, muscle weakness, bone damage, fluid retention and facial rounding. Irregular heartbeat and vision problems are also among the potential serious side-effects.

Doctors may also prescribe immune suppressants to subdue the production of antibodies.

Once a patient is treated, they can go into partial remission after several weeks to several months. During this partial remission, people must still take a reduced dose of immune suppressants.

The disease has been described as very painful. Patients report a severe burning feeling, like being "dragged behind a car" or being scalded with water.

To prevent the blisters from rubbing, bursting and sticking the skin to their clothes, patients often wear gauze between their skin and clothes.

Bullous pemphigoid can appear in the mucous membrane, causing lesions in the larynx, pharynx, tongue, nose and eyes.

The disease is rare, with an estimated prevalence of one in 40,000, according to Orphanet.

Sources: Canadian Pemphigus and Pemphigoid Foundation, U.K. National Health Service, A.D.A.M. Medical Encyclopedia, Orphanet, Canadian Medical Association New Guide to Prescription and Over-the-counter Drugs

With files from The Canadian Press