WASHINGTON, D.C. - A Minnesota congressman is calling for a nationwide investigation to determine how many unqualified Veteran's Administration doctors have been doing traumatic brain injury (TBI) exams.

The request comes in the wake of disclosures that unqualified doctors performed hundreds of TBI exams at the Minneapolis VA's Compensation and Pension (C&P) Department. Those exams resulted in veterans being improperly denied benefits.

In a letter to the Inspector General for the Department of Veterans Affairs, Rep. Tim Walz (D-MN) says he's concerned that problems exposed at the Minneapolis Veterans Medical Center may exist "throughout the VA system."

"It's certainly possible if it happened in Minneapolis it's possible, and I would argue probable, it happened elsewhere," Walz told KARE 11's A.J. Lagoe late Wednesday.

VA policy says that initial TBI exams must be done by doctors in one of four specialties – including neurology and neurosurgery.

In recent weeks, however, KARE 11 has documented cases in which veterans were examined by unqualified medical personnel.

Butch Hamersma, a Vietnam veteran now farming near Spring Valley, Minnesota, was denied TBI benefits after an exam done by a nurse practitioner, not a neurologist.

His denial of benefits came in spite of combat medical records showing Hamersma's skull was shattered in an explosion near Chu Lai in November, 1968.

"Run over a land mine," he recalled. "Three days later I woke up in Japan."

According to an internal memo, the exams done in violation of VA policy went on for years.

In an email to his staff one day after KARE 11 reported Hamersma's story, Minneapolis VA Health Care Systems Director Patrick Kelly wrote, "It's true that we used the wrong type of examiner on some initial TBI exams from 2010-2014."

Rep. Walz says the actual number of veterans impacted by the improper exams is more than 300.

In fact, KARE 11 has documented a case in which a veteran was denied benefits not once, but twice, after being examined by two different unqualified doctors.

Finally, after multiple appeals, the veteran was given a third examination. A qualified specialist diagnosed the TBI and he's now receiving benefits.

In a written statement to KARE 11, Minneapolis VA Public Information Officer Ralph Heussner said last month that veterans who were not seen by specialists were being offered new examinations, adding "we greatly regret the inconvenience to Veterans who returned for a repeat evaluation."

Rep. Walz calls traumatic brain injuries "the signature wound" of the wars in Iraq and Afghanistan, so it's "essential" to know if unqualified doctors have been doing TBI exams at other VA facilities across the country.

"I want to know that every veteran that went in to do a C & P exam and specifically being screened for TBI saw a qualified medical professional," he told KARE 11.

An attempt to determine the scope of the problem, KARE 11 and other TEGNA television stations began filing Freedom of Information Act requests in July asking for the names and qualifications of medical personnel who had performed initial TBI exams at VA Medical Centers.

However, in the wake of the Minneapolis disclosures, the Department of Veterans Affairs is refusing to release the names claiming it would violate "personal privacy."

Without those names, it's virtually impossible to independently verify whether the doctors were properly qualified.

KARE 11 and our parent company TEGNA are appealing the VA's FOIA denial, arguing that releasing the names of the doctors who have performed initial TBI exams will allow thousands of veterans and the public to determine how often exams by unqualified doctors may have denied Veterans benefits and access to medical care.