The self-insured employer appeals the compensation judge’s finding that the employee’s medication expenses were causally related to the employee’s work injury and the compensation judge’s refusal to require the employee’s treating physician to respond to the employer’s request for an opinion on causation.  We affirm.

On January 31, 1978,^[1] Clifton Moore, the employee, sustained a work-related injury to his low back while employed by the University of Minnesota, the employer, which was self-insured for workers’ compensation liability.  In February 2000, the employee underwent a three-level anterior/posterior lumbar fusion procedure, with hardware, performed by Dr. Glenn Buttermann.  In July 2004, the parties entered into a stipulation for settlement on a to-date basis, in which the employer agreed that the employee’s 1978 work injury was a substantial contributing cause of his need for the surgery in 2000.

The employee initially reported nearly complete relief post-surgery from his symptoms, but later reported that his low back and leg pain had recurred.  In August 2004, the employee was seen by a physician assistant to Dr. Buttermann; he reported increased pain and erectile dysfunction.  On September 17, 2004, the employee consulted Dr. Buttermann regarding increased low back pain, occasional right leg symptoms and erectile dysfunction symptoms.  In his office note from that visit, Dr. Buttermann outlined the symptoms reported by the employee, and stated that the employee’s increased low back pain and right leg numbness, as well as his tenderness over the pedicle screw heads, might be related to his SI joints, but that, even if that were the case, he would recommend removal of surgical instrumentation before an additional diagnostic work-up of his SI joints.  Dr. Buttermann also stated that he and the employee “also discussed his erectile dysfunction which is related to his back condition.  He was given a prescription for Cialis.”  (Emphasis added.)

In December 2004, the employee underwent surgery to remove the fusion hardware.  Although his fusion remained solid, he developed right thigh pain, which Dr. Buttermann diagnosed in February 2005 as meralgia paresthetica,^[2] and for which he prescribed a Medrol Dosepak.  Dr. Buttermann also gave the employee another prescription for Cialis, with three refills, but he advised the employee that “he should get this from his primary care physician or urologist in the future.”

In July 2005, the employee was examined by Dr. Paul Cederberg, an orthopedic surgeon, at the employer’s request.  Dr. Cederberg stated that he could not discern any evidence in the employee’s medical records that proved his erectile dysfunction was related to his low back condition, and that there were other possible causes of that condition.  Dr. Cederberg also stated that it was beyond Dr. Buttermann’s field of expertise, or his own expertise, to prescribe medication for erectile dysfunction.

Through a medical request, the employee claimed payment for medical expenses incurred for the prescribed Cialis.  The employer objected, and the matter came on for hearing before Compensation Judge Rolf Hagen on August 3, 2005.  At the hearing, the employee testified that he had never experienced any problem with erectile dysfunction before the fusion surgery, that his first attempt at sexual relations after the surgery was very painful, and that the Cialis prescription had allowed him to engage in intercourse.  Dr. Buttermann’s records and Dr. Cederberg’s report were submitted into evidence at the hearing.

In Findings and Order served and filed September 19, 2005, Compensation Judge Rolf Hagen concluded that the employee’s erectile dysfunction was causally related to his work injury and that the prescribed Cialis was reasonable and necessary to treat that condition.  The employer appealed to this court, arguing, in part, that the compensation judge erred in accepting the causation opinion of Dr. Buttermann, in that he did not conduct a urologic examination and that Dr. Buttermann, as an orthopedic surgeon, was simply not qualified to render either a causation opinion or treatment with respect to the employee’s alleged erectile dysfunction.  In a decision served and filed on February 7, 2006, this court affirmed the compensation judge’s award of medical expenses, noting that Dr. Buttermann had been the employee’s primary treating physician for years prior to giving him the Cialis prescription in September of 2004, and that as “a medical doctor familiar with the employee’s low back condition and an orthopedic surgeon with substantial experience with low back injuries and treatment, Dr. Buttermann clearly had adequate foundation to render an opinion tying the employee’s erectile dysfunction to his low back condition and resulting pain.”  Moore v. University of Minnesota, No. WC05-268 (W.C.C.A. Feb. 17, 2006).

In August 2005, the employee consulted Dr. Daniel Reeves at the Quello Clinic, where, according to the employee’s testimony, the employee had received a portion of his medical treatment since 1994.  Dr. Reeves had performed a pre-operative physical examination on the employee before his 2004 surgery, and the employee had consulted him following his surgery.  Dr. Reeves diagnosed chronic low back pain, depression, and erectile dysfunction and prescribed Cialis.

In October 2005, Dr. Reeves’s office was contacted by a representative of Injured Workers Pharmacy, the insurer’s pharmacy provider who has intervened in this dispute, requesting clarification on how the Cialis prescription pertained to the employee’s workers’ compensation claim.  Dr. Reeves noted on the employee’s medical chart that he would need to speak with the employee first to ensure that he had permission to speak with the pharmacy provider.  A representative from Quello Clinic relayed that message to the pharmacy representative, who then responded that she needed to seek permission from the insurance adjuster before approving the prescription.  The medical chart notes contain no additional reference to these communications between the Quello Clinic and the pharmacy provider.

In March 2006, the employee was evaluated by Dr. James Meyer, a urologist, at the employer’s request.  Dr. Meyer opined that the employee’s 1978 work injury was not a significant factor in the employee’s reported erectile dysfunction condition and that there were other likely causes including the employee’s history of cigarette smoking, his age or psychological causes.  Dr. Meyer commented that the employee “may very well have erectile dysfunction, but that there has been no objective testing and he has not seen an urologist.”  Dr. Meyer also stated that he found no objective evidence that the employee’s back injury or his spinal surgery was causally related to his erectile dysfunction and also commented that his current treatment was adequate and that he should continue to use Cialis.

On June 2, 2006, the employee filed a medical request for the cost of the Cialis prescribed by Dr. Reeves.  The employer denied the request, and an administrative conference was held on August 2, 2006; the expenses were awarded.  The employer requested a formal hearing, which was then scheduled to be held in November 2006.

On October 17, 2006, the claims examiner for the self-insured employer’s claims administrator wrote to Dr. Reeves requesting his opinion on whether the employee’s Cialis prescription was causally related to the employee’s low back condition.  In that letter, the claims examiner stated, in part, as follows:

On November 22, 2006, a formal hearing was held before Compensation Judge Harold Schultz, II, to address the employee’s medical request.^[4]  At the hearing, the employee moved for a decision on the pleadings, arguing that the issue of whether the employee’s erectile dysfunction was causally related to his work injury had been determined by a compensation judge in the earlier decision and affirmed by this court, and therefore could not be decided differently under principles of res judicata.  The compensation judge denied this motion, and the hearing proceeded on the merits of the claim.  At the hearing, the employer attempted to elicit the employee’s authorization to solicit a causation opinion from Dr. Reeves.  The employee objected and the compensation judge sustained the objection.  In his findings and order served and filed on December 14, 2006, the compensation judge found that the employee’s erectile dysfunction condition was causally related to the employee’s 1978 work injury and awarded the claimed prescription medical expenses.  The employer appeals.

The self-insured employer attempted to solicit an opinion on causation from the employee’s treating physician, Dr. Reeves.  The employer wrote directly to Dr. Reeves, asking him whether the employee’s work-related low back condition was causally related to the Cialis prescription.  By letter to Dr. Reeves, the employee’s attorney advised the doctor that he was not required to respond to the employer’s inquiry.

On appeal, the employer cites to the rules governing workers’ compensation practice and procedure in Minnesota, and contends that under Minn. R. 1420.2200, subp. 1.C., an employee waives his or her medical privilege in litigation before the Office of Administrative Hearings.^[5]  The employer argues that the employee’s refusal to allow the employer to solicit the treating physician’s opinion on causation is tantamount to a withdrawal of the waiver of medical privilege required under the workers’ compensation act, and that the employer should be able to solicit an opinion from the treating doctor where the doctor’s opinion is not available in the existing medical records.  The employer also argues that the employee has blocked the employer from receiving an explanation from the prescribing doctor about the disputed medical treatment, and that a fair workers’ compensation hearing “cannot be conducted if the Employee will not waive his medical privilege regarding the physician prescribing the medical treatment at issue.”  (Employer’s brief, p. 3.)  We disagree.

In a workers’ compensation action, an employee is protected by federal constitutional and statutory rights of privacy and patient/doctor privilege against an employer’s unauthorized direct communication with the employee’s treating doctor, with only a few qualified exceptions provided by the Minnesota workers’ compensation act.  Eggert v. Northern States Power Co., slip op. (W.C.C.A. May 14, 1991) (interpreting an earlier version of the relevant statute).  Under Minn. Stat. § 176.138(a), nonwritten medical data - - such as an opinion concerning causation as was requested by the employer in this case - - is not required to be provided by the possessor of that data.  As a result, Dr. Reeves was within his rights to refuse to respond to the employer’s inquiry and request for an opinion.  Further, the employee did not improperly impede Dr. Reeves from responding to the employer’s inquiry.

We see no prejudice to the self-insured employer in this situation.  Minn. Stat. § 176.155, subd. 5, provides an exception available to an employer or insurer for obtaining an opinion from a treating physician.  Under that section, a party “may cross-examine by deposition a physician or health care provider who has examined or treated the employee.”  Therefore, absent a subpoena or a notice of taking deposition, a treating physician is not required to provide nonwritten medical data, such as a causation opinion, to an employer or insurer.  In this case, the employee authorized the employer to obtain his existing medical records, but objected to the employer’s request to Dr. Reeves that he provide the employer with his opinion concerning the causation of the employee’s erectile dysfunction.  We conclude that Dr. Reeves was not required by the statute to provide his opinion.

The employer also appeals the compensation judge’s finding that the employee’s erectile dysfunction condition and need for medication are causally related to his 1978 work injury.  An employee has the burden of proving that claimed medical expenses are reasonable, necessary, and causally related to his work injury.  Adkins v. University Health Care Ctr., 405 N.W.2d 233, 39 W.C.D. 898 (Minn. 1987).  The employee relied upon the opinion of Dr. Buttermann that a causal relationship existed.  Dr. Meyer, however, concluded that the employee’s 1978 work injury was not a significant factor in the development of his erectile dysfunction condition, and that there are other likely causes of that condition.  The employer argues that Dr. Meyer’s opinion is more persuasive than the opinion of Dr. Buttermann, the employee’s treating surgeon, since Dr. Meyer is a urologist.  The employer also contends that Dr. Meyer’s opinion should be accorded more weight as he alone conducted a urological examination of the employee, in contrast to Dr. Reeves and Dr. Buttermann, whom the employee admitted had not conducted such an examination.  Dr. Buttermann was familiar with the employee’s condition, having treated him for many years, and whether a doctor is a specialist goes to the weight of the doctor’s opinion, and is not a determinative factor.  See Drews v. Kohl’s, 55 W.C.D. 33, 40 (W.C.C.A. 1996); see also Stuhr v. Northwestern Travel Serv., Inc., 57 W.C.D. 352 (W.C.C.A. 1997), summarily aff’d (Minn. Dec. 15, 1997).  Questions of medical causation fall within the province of the compensation judge.  Felton v. Anton Chevrolet, 513 N.W.2d 457, 50 W.C.D. 181 (Minn. 1994).  It is the compensation judge's responsibility, as trier of fact, to resolve conflicts in expert testimony, and his choice between experts whose testimony conflicts is usually upheld unless the facts assumed by the expert in rendering his opinion are not supported by the evidence.  Nord v. City of Cook, 360 N.W.2d 337, 37 W.C.D. 364 (Minn. 1985).  Contrary to the employer’s arguments that the compensation judge had no basis for relying on Dr. Buttermann’s opinion concerning causation, we conclude that the judge did not err by relying on his opinion.

The employee argues that the issue of whether his erectile dysfunction was causally related to his work injury has been determined and therefore, under principles of res judicata, the earlier determination of a causal relationship is final.  Res judicata is a doctrine bringing finality to legal proceedings in which "a final judgment on the merits bars a second suit for the same claim” by the same parties.  Kaiser v. Northern States Power Co., 353 N.W.2d 899, 902 (Minn. 1984).  Principles of res judicata are applicable in workers’ compensation proceedings.  See, e.g., Alexander v. Kenneth R. LaLonde Enters., 288 N.W.2d 18, 31 W.C.D. 407 (Minn. 1980).  However, res judicata applies in workers’ compensation cases only with respect to issues specifically litigated and decided in prior proceedings.  See, e.g., Fischer v. Saga Corp., 498 N.W.2d 449, 450, 48 W.C.D. 368, 369 (Minn. 1993); see also Westendorf v. Campbell Soup Co., 243 N.W.2d 157, 158, 28 W.C.D. 460, 460 (Minn. 1976).

While the claimed prescription medical expenses in the present case were dated after the 2005 hearing, the issue of whether the employee’s erectile dysfunction was causally related to the employee’s work injury was directly litigated and decided at the 2005 hearing and was affirmed by this court.  The employee moved for a decision on the pleadings based on the principles of res judicata at the hearing.  The compensation judge denied the motion and the hearing was held.   In his Findings and Order, however, the compensation judge noted that there was only a short time between the litigation on the employee’s prior claim - - that his need for prescription medication to treat erectile dysfunction was causally related to his work injury, which had been decided in the employee’s favor - - and this current claim.  The judge also found that there was no other injury or event since that earlier litigation which would lead to a different result.  The compensation judge acknowledged the effect of the earlier decision on his determination in this case, stating, in his memorandum that,

In reaching his conclusions, the compensation judge relied on the outcome of the earlier litigation, Dr. Buttermann’s opinion and the employee’s testimony that the prescribed medication was effective.  Substantial evidence in the record supports the compensation judge’s finding that the employee’s erectile dysfunction condition, and his need for the claimed medication, are causally related to the employee’s 1978 work injury.  Accordingly, we affirm.