Anaheim-based Questcor Pharmaceuticals Inc. will start marketing its core Acthar drug for rheumatoid arthritis and related conditions.

The drug maker is going to begin a pilot sales program by mid-July that will start out with the hiring of 12 salespeople and an initial concentration on a pair of rare inflammatory neuromuscular disorders, dermatomyositis and polymyositis.

Questcor said that it plans to market Acthar, which is approved for 19 conditions, to as many as 1,000 neurologists who specialize in treating neuromuscular diseases by late this year.

The company is expanding Acthar marketing because its other approved uses offer the potential to help more patients, Chief Executive Don Bailey said on a conference call.

“We believe that these markets together form a several-billion-dollar market opportunity,” Bailey said.

Acthar's uses include nephrotic syndrome, a kidney disease, and to treat multiple sclerosis flares.

The drug maker’s shares got a boost after last week’s announcement. Questcor shares are up 3% today to a market value of about $3.2 billion.