Carpal tunnel syndrome is a common affliction, but other entrapment neuropathies can be masquerade as carpal tunnel syndrome.
Pronator syndrome (also known as pronator teres syndrome) is an entrapment neuropathy of the median nerve that occurs at the level of the elbow. Other entrapment neuropathies of the median nerve are the supracondylar process syndrome, anterior interosseous nerve syndrome, and carpal tunnel syndrome.
Here is a patient with pronator syndrome. There is edema in the pronator teres and FCR (red arrows) and abnormal signal in part of flexor digitorum superficialis (green arrow). There is also edema in the muscles innervated by the anterior interosseous nerve branch of the median nerve, including the flexor pollicis longus and flexor digitorum profundus (white arrows).
Many people expect to find a mass in these cases, but things are usually like the Wonder-Bra: you see the result, but the cause is hidden.