Slaughterhouse workers sickened by inhaling aerosolized pig brain have shown substantial improvement in their symptoms, and some have even gone back to work, according to the follow-up of 24 patients first described more than 1 year ago.

Dozens of men and women working in three U.S. pork processing plants in the Midwest developed a neurologic illness characterized by fatigue, malaise, weakness, pain and tingling in the arms and legs. A doctor in Austin, Minnesota, where one of the plants is located, first alerted investigators from the Mayo Clinic after seeing several patients with similar symptoms.

Minnesota Department of Health investigators determined that the ill patients had all worked at the pork processing plant's "head table," which used compressed air to blast brain tissue out of pig skulls. The plants using the brain-blasting technique, which included one in Indiana and one in Nebraska as well as the Austin facility, volunteered to stop after learning that it might be making workers sick.

Drs. P. James B. Dyck and Daniel H. Lachance, neurologists at the Mayo Clinic who have been following workers with the disorder, will present an update on the workers' health at the American Academy of Neurology's upcoming annual meeting.

"By all objective measures they're a lot better than they were before," Dyck told Reuters Health. The two workers who were the sickest — one with encephalitis, and another with a disorder of the spinal cord — have gone back to work. But many of the workers continue to have pain, Dyck added, and none are completely back to normal.

The Mayo Clinic team determined that the workers developed a new type of sensory predominant polyradiculoneuropathy. A previously undescribed antibody was isolated from all of the patients. The investigators suggest that the disorder is autoimmune in origin - with the patients developing an immune reaction in which their own nervous system is attacked.

Neurological testing in the patients had revealed many abnormalities, including changes in nerve impulse conduction, sensory nerve function and body temperature regulation.

Seventeen of the patients received treatment to blunt their autoimmune response, including steroids, immunoglobulin, or other therapies. Twelve of them showed "marked" improvement, while four more had moderate or mild improvements and one worker has not yet been re-evaluated. Among the seven patients who didn't receive immune treatment, six got better on their own, and one was lost to follow-up.

None of the patients are completely symptom-free, the researchers note, and many still have some pain.

Dyck, Lachance and their colleagues are hoping that by studying this outbreak of a new illness — which seems to have been limited to workers at the three plants — they will learn more about other illnesses that cause similar kinds of nerve damage, such as Guillain-Barré syndrome, chronic inflammatory demyelinating neuropathy.

They also hope to learn more about a rare group of conditions called paraneoplastic disorders, in which patients undergoing treatment for cancer develop immune-related nervous system disease.