Doctors suspected man had brain cancer. He actually had worms.

A  60-year-old man in Spain went to the doctor complaining of a headache that he couldn't shake. It had started two weeks prior and was only getting worse. He also said he had noticed subtle changes in his behavior.

In a neurological exam, doctors found he had a mild delay in his movements, but no other deficits. His blood work was generally normal except for elevated IgE, a signal of immune responses linked to allergies, autoimmune disease, and parasitic infections. The doctors did a computed tomography (CT) scan of his head and saw much more obvious evidence of a problem: There were multiple lesions distributed throughout his brain accompanied by swelling.

In a case report in Emerging Infectious Diseases, the doctors reported working through the possible conditions that could explain all the findings. They noted that the man was not immunocompromised and had never traveled internationally. Their top suspicion was metastatic cancer.