Proving Medical Causation: Why “May” Loses and “More Likely Than Not” Wins

Most workers’ compensation claims in Nebraska are not lost on the facts. They are lost on a sentence in a doctor’s letter — a sentence the doctor thought was careful and the law reads as nothing. “The injury may have contributed.” “It is possible the fall aggravated his condition.” “Treatment could have prolonged her life.” Each is an honest medical statement. Each is, under Nebraska law, insufficient to support an award. In May 2026 the Nebraska Supreme Court affirmed the denial of death benefits to a widow whose husband’s cancer treatment was derailed by a work injury, on exactly that ground, and the opinion is the clearest recent statement of what a medical opinion has to say to carry a claim. This page explains the rule, walks through that case, and lays out how I work with treating physicians so that the opinion in the file says what the law requires.

The Rule: Proof, Not Certainty — but Not Possibility Either

A Nebraska claimant must prove by a preponderance of the evidence that the employment proximately caused the injury and the disability, or the death, for which benefits are claimed. Unless the nature and effect of the injury are plainly apparent — a laceration from a saw, a fracture from a fall — that proof must come from expert medical testimony showing the causal connection between the injury and the claimed disability. The Supreme Court has been precise about what that testimony must sound like, and it has been precise in both directions. A physician does not have to use the magic words “reasonable medical certainty” or “reasonable probability”; the court reads the opinion as a whole and asks whether it establishes the causal link. And the claimant does not have to prove causation with absolute certainty; the court said so in 1965 and repeated it in 2026. But an opinion expressed in terms of what “could,” “may,” or “possibly” happened — in the court’s phrase — “lacks the definiteness required to support an award from the Workers’ Compensation Court.”

The line, then, runs between probability and possibility. The court has defined the threshold in plain English in the parallel medical-malpractice context: causation testimony “must be stated as being at least ‘probable,’ in other words, more likely than not” (Carson v. Steinke, 2023). “More likely than not,” “in my opinion the work injury caused,” “I attribute this condition to,” “to a reasonable degree of medical probability” — these are opinions. “May have,” “might,” “possibly,” “could be related,” “cannot rule out” — these are speculation, however sincere, and a compensation judge is not permitted to build an award on them.

The Case: Hastreiter v. Foltz Brothers (2026)

Thomas Hastreiter was diagnosed with urothelial carcinoma in December 2021 and kept working as a truck driver and farm laborer. On September 26, 2022, he fell at work and injured his left hip. Three days later, while he was hospitalized for the hip, his oncologist told him the cancer had spread, described it as “incurable but treatable,” and recommended immunotherapy once he recovered from the injury. He never recovered from it. Hip surgery led to an infection, the immunotherapy never started, and he died on December 14, 2022. His death certificate listed progressive metastatic cancer as the immediate cause and stated that complications and infection from the hip injury had delayed treatment, “resulting in progression of cancer.”

The compensation court did what the law required on the injury itself: it awarded temporary total disability from the day after the fall through the day of death, because the hip made him unable to work “regardless of the cancer,” along with medical expenses and fees. What it denied was the widow’s claim for death benefits, finding that he “died as a result of his pre-existing cancer.” The Supreme Court affirmed unanimously.

The decision turned entirely on three doctors’ letters. The treating oncologist wrote that earlier immunotherapy “may have made a difference in prolonging [his] life (assuming that immunotherapy was effective).” The court called that opinion “insufficiently definite” without hesitation: the doctor “hedged his opinions in more ways than one.” The employer’s oncologist wrote that the injury did not cause, aggravate or accelerate the cancer, that the treatment “can prolong survival,” that Thomas “may have lived longer,” and — the widow’s best evidence — that he “would have estimated his survival to be 3-6 months” with treatment; Thomas died in under three. The court read that estimate in context: it was given in answer to a question asking whether Thomas “might” have lived three to six months, and “a statement that Thomas ‘might’ have lived another 3 to 6 months is, in substance, no different than a statement that he ‘may’ have.” The estimate, the court observed, “appears to carefully stop short” of an opinion to a reasonable degree of medical probability that he would have lived longer. The third physician, a physiatrist, simply agreed with the second’s “may have lived longer,” which inherited the same defect.

The court did not decide whether a “lost chance” of extended life can ever support death benefits in Nebraska; it assumed so for purposes of the appeal and held that, even on that assumption, the widow had not proven with sufficiently definite medical testimony that her husband would have lived longer. The theory was never reached because the proof never arrived.

The Second Lesson: Even a Good Opinion Can Be Disbelieved

Hastreiter also restates a rule that surprises clients. The compensation court is the sole judge of which experts to believe, and it may decline to credit an expert opinion even when no one contradicts it. The Supreme Court cited a 1991 case in which the compensation court rejected unrefuted testimony that a back injury was work-related and was affirmed, and it explained that the only exception is narrow: testimony so “unassailable” — based on firsthand knowledge, credible, with no demonstrable weakness or failure of foundation — that the judge clearly errs by ignoring it. An expert who examined the records rather than the patient, who answers leading questions with “correct,” or whose letter’s “main focus” cuts the other way does not clear that bar. Definiteness gets an opinion into evidence; foundation and credibility decide whether it wins.

Where the Same Rule Decides Other Claims

The “may” problem is not confined to death benefits. It decides the contested question in almost every claim I handle, and the pattern is the same each time.

Pre-existing conditions. Nebraska’s aggravation rule is generous — a work injury that lights up or worsens a dormant condition is compensable in full, and the statute excludes only disability that is the “natural progression” of the pre-existing condition. The whole fight is causation: was the new disability the direct and natural result of the accident, or the progression that would have happened anyway? A treating physician who writes that the fall “may have aggravated” a degenerative spine hands the carrier the natural-progression argument. The opinion has to say that, more likely than not, the accident caused the worsening. My pre-existing conditions page covers the doctrine; this page covers the sentence that makes it work.

Psychological consequences. Depression, anxiety or chronic pain flowing from a physical injury are compensable, but the burden is on the worker to prove the connection by medical evidence, and the Supreme Court has held a psychological claim “simply not a factor” where the worker “never attempted to prove a causal relationship.” The depression and chronic pain page shows the cases won and lost on the doctor’s wording.

Repetitive trauma and occupational disease. Where there is no single accident, the physician has to connect the condition to the work activity itself, and “consistent with” or “could be work-related” is the language carriers deny on. Repetitive trauma claims are causation claims first.

Permanency and future medical. Whether a restriction, an impairment rating or a proposed surgery is attributable to the work injury is an expert question; a 2026 Court of Appeals decision affirmed the denial of permanent disability and future medical where the worker’s own physicians attributed her migrating pain to a somatization disorder and the employer’s examiner found no ongoing injury to a reasonable degree of medical certainty. The carrier’s examiner will use the magic words even though the law does not require them; the treating physician had better be at least as clear.

The Phrases That Pass and the Phrases That Fail

Because the compensation court reads an opinion as a whole, no single formula is required, but the pattern in the decided cases is consistent enough to state. Language the courts have accepted: “in my opinion, the work injury caused”; “the accident aggravated the pre-existing condition and is the reason for the current restrictions”; “more likely than not”; “to a reasonable degree of medical probability”; “I attribute the need for surgery to.” Language the courts have rejected as insufficiently definite: “may have contributed”; “could be related”; “possibly aggravated”; “might have”; “it is conceivable”; “cannot rule out.” And a category in between that Hastreiter flags: a confident-sounding estimate given in answer to a question framed with “might,” which the court will read as adopting the questioner’s hedge. Whoever drafts the question to the doctor is drafting the answer.

Two decisions show the rule’s other edge — that the court reads the whole opinion and that a deficient letter can be cured. In Prinz v. Omaha Operations (2024), a treating physician wrote that there was “reasonable degree of medical certainty” that a worker’s asthma and a workplace exposure were “associated” because no other trigger had been identified; the employer argued “associated” was not causation, and the Supreme Court affirmed the award, holding the opinion must be judged from the expert’s entire statement and the record as a whole. In Moss v. C&A Industries (Neb. App. 2018), one physician’s letter used “could” and “may” and was held insufficient, while a second physician who had used the same words “cleaned up the deficiencies” with a follow-up report stating that the knee injury was the result of the accident — and that opinion carried the claim. The first letter is rarely the last word, if someone reads it in time.

Why Doctors Write “May”

Physicians hedge for good reasons that have nothing to do with the claim. Medicine is probabilistic; a careful doctor is trained not to overstate; a letter written to a lawyer feels like a document that could be used against them; and no one has explained that the legal standard is probability, not certainty, and that “more likely than not” is a statement most treating doctors are entirely comfortable making once they understand that is the question. The oncologist in Hastreiter almost certainly believed that earlier treatment would probably have extended his patient’s life. He wrote “may,” and the widow lost.

How I Get the Opinion Right

The work is done before the letter is written, not after. First, the question is framed correctly: the physician is asked whether, in their opinion and more likely than not, the work accident caused the condition, aggravated it, or caused the need for the treatment — and told that this is the legal standard, that certainty is not required, and that “possible” is not an answer. Second, the physician gets the foundation: the mechanism of injury, the prior records, the imaging, the timeline — because an opinion that recites what the doctor reviewed survives cross-examination and one that does not is the “failure of foundation” the court described. Third, the opinion addresses the defense theory head-on: if the carrier’s examiner will say natural progression, the treating physician explains why the timeline and the findings are not that. Fourth, the language is checked before it is signed. A letter that says “may” is sent back with a conversation, not filed with a hope. And fifth, the opinion is tested against Hastreiter’s second lesson: is it unassailable enough that a judge would clearly err in ignoring it? If the answer is no, the file needs a second opinion, a deposition, or better foundation before trial, not after.

What This Means for an Injured Worker

Tell your doctor the whole mechanism of injury, every time, and tell the truth about your history — a physician who learns about a prior back problem from the carrier’s examiner rather than from you cannot write a credible aggravation opinion. Understand that the denial letter that says “the medical evidence does not support causation” is often a comment on a sentence, not on your injury. And do not let a claim go to hearing on a “may.” The compensation court will not be able to help you, however sympathetic the facts, because the Supreme Court has told it that it cannot.

If your claim has been denied on causation, or a doctor’s letter in your file reads like the ones in Hastreiter, call (402) 378-9208 or send a message. The consultation is free, there is no fee unless I recover for you, and reading a medical opinion for the words that will decide the case is the first thing I do with every file. The denied claims page explains what happens after a denial; the IME page explains the examiner whose letter will use the magic words against you.

Your Attorney

Frank Younes

Every page on this site is written by Frank Younes, a Nebraska trial attorney with a published record of verdicts and settlements, selection to the National Trial Lawyers Top 100, and a practice that covers every county in Nebraska and Iowa. No case is handed to an associate — the lawyer you read here is the lawyer who works your case.

More about Frank → · Free consultation: (402) 378-9208

Frequently Asked Questions

Does my doctor have to say “reasonable degree of medical certainty”?

No. The Supreme Court has said those magic words are not required; the opinion is read as a whole. But it must express probability, not possibility — “may,” “could” and “possibly” lack the definiteness required to support an award.

What happened in Hastreiter v. Foltz Brothers?

A worker with cancer fell at work in 2022, hip surgery led to an infection, his immunotherapy never started, and he died. His widow’s death-benefits claim was denied because the doctors said treatment “may” have prolonged his life; the Supreme Court affirmed in May 2026. His disability benefits for the hip were paid.

Did the court decide whether a “lost chance” of longer life is compensable?

No. It assumed the theory was valid for purposes of the appeal and held the proof failed anyway. The question remains open in Nebraska.

Can the compensation court ignore my doctor if the carrier has no contrary expert?

Yes. The compensation court decides which experts to believe and may decline to credit even undisputed testimony, unless the opinion is so well-founded and credible that ignoring it would be clear error.

Do I have to prove causation with certainty?

No. The standard is a preponderance of the evidence — more likely than not. Absolute certainty is not required, and the Supreme Court said so again in 2026.

My claim was denied for “insufficient medical evidence.” Is it over?

Usually not. Denials on causation are frequently about the wording or foundation of one letter, both of which can be fixed before a hearing with the right questions to the treating physician.