NEW YORK (AP) — Biotechnology companies Biogen Idec Inc. and Elan Corp. on Monday reported the fourth case this year of a deadly brain infection in a patient taking their multiple-sclerosis drug Tysabri. The companies said they notified relevant regulatory agencies about the patient, located in the European Union, on Dec. 11. That patient has received about 26 months of Tysabri for the autoimmune condition multiple sclerosis and is being treated by a physician. The drug has been facing pressure on the market since August, when the companies reported two new cases of the brain infection called progressive multifocal leukoencephalopathy, or PML. A third case was reported in November. More than 35,500 patients are taking the drug worldwide. The companies have argued the risks, which are on the drug’s label, are outweighed by the benefit the drug provides to multiple sclerosis patients. Tysabri was pulled from the market in 2005 after being linked to PML but reintroduced under restricted sales conditions in mid-2006. Shares of Cambridge, Mass.-based Biogen fell 58 cents to $46.52 in morning trading. Shares of Ireland-based Elan suffered the most, shedding 27 cents, or 3.8 percent, to reach $6.92. The new case of PML comes on top of investor calls for management change at Elan, a restructuring move by the company and a class-action lawsuit. On Friday, Elan said it would close offices in New York and Tokyo during the first quarter and cut jobs as it changes marketing activities for Tysabri. Meanwhile, it faces a class-action lawsuit by the firm Barroway Topaz Kessler Meltzer & Check LLP in U.S. District Court for the Southern District of New York. Late Friday, CrabTree Partners co-founder Jack Schuler asked Elan’s board of directors to remove Chief Executive Kelly Martin and other executives, citing poor management. The stock is down about 67 percent since the beginning of January. Martin owns about 1 percent of Elan’s stock.