A drug already on the market that treats immune disorders may help stabilize patients with Alzheimer’s disease for up to three years, according to the results of a tiny study presented at a conference on Tuesday.

All four patients who received the optimal dose of the drug, Gammagard from Baxter International, had no decline in several measures of cognition and daily function for three years, researchers said.

Dr. Norman Relkin of Weill Cornell Medical College, the lead investigator of the study, said the results were “remarkable” because patients with Alzheimer’s disease typically worsen within 12 months.

“If we have a patient who goes 18 months without changing we begin to doubt they have Alzheimer’s,” Dr. Relkin said in a news conference at the Alzheimer’s Association International Conference in Vancouver, British Columbia, where the results were presented.