Two drugs Anna Nicole Smith reportedly was taking may have been prescribed if she were suffering from lupus, an expert in New York told "Access Hollywood."

An official cause of Smith's death has not been determined. Before her death, she reportedly used Topamax, Dilaudid and Methadone, according to testimony in a Florida hearing on her burial.

These drugs normally aren't prescribed for lupus, a disease affecting the immune system. Pregnancy combined with lupus, however, could present severe pain, according to the expert contacted by "Access Hollywood."

Bob Lahita, a physician and professor of medicine at Mount Sinai Medical School, said about 60 percent of lupus patients develop fibro myalgia, which can cause chronic and extreme pain all over the body, "Access Hollywood" reported.

Sleeping can be difficult because of the pain, so Topamax and Dilaudid may have been used for comfort, Lahita told "Access Hollywood."

Smith gave birth to her daughter last fall. If she had lupus, the symptoms of lupus three months after delivery can "really flair up," he told "Access Hollywood."

Lahita said he has been contacted by at least one other media outlet since claims Smith had the disease began to surface.