Under the "last exposure rule", workers' compensation liability for occupational disease of carpal tunnel syndrome fell on employer in whose employment employee was last exposed to hazard of the disease prior to the filing of the claim, and not on subsequent employer. Johnson v. Denton Const. Co., 911 S.W.2d 286 (Mo. 1995).
An informative legal analysis of occupational diseases pursuant to the Missouri statutes is found in Kelley v. Banta and Stude Construction Co., Inc., 1 S.W.3d 43 (Mo. App. E.D 1999), from which the following legal principles are cited:
[1,2] In order to support a finding of occupational disease, employee must provide substantial and competent evidence that he/she has contracted an occupationally induced disease rather than an ordinary disease of life. Hayes v. Hudson Foods, Inc., 818 S.W.2d 296, 299-300 (Mo. App. 1991). The inquiry involves two considerations: (1) whether there was an exposure to the disease which was greater than or different from that which affects the public generally, and (2) whether there was a recognizable link between the disease and some distinctive feature of the employee's job which is common to all jobs of that sort. Polavarapu v. General Motors Corp., 897 S.W.2d 63, 65 (Mo. App. E.D. 1995); Dawson v. Associated Electric, 885 S.W.2d 712, 716 (Mo. App. W.D. 1994); Hayes, 818 S.W.2d at 300; Sellers v. Trans World Airlines, Inc., 752 S.W.2d 413, 415 (Mo. App. 1988); Jackson v. Risby Pallet and Lumber Co., 736 S.W.2d 575, 578 (Mo. App. 1987).
[3-6] Claimant must also establish, generally through expert testimony, the probability that the claimed occupational disease was caused by conditions in the work place. Dawson 885 S.W.2d at 716; Selby v. Trans World Airlines, Inc., 831 S.W.2d 221, 223 (Mo. App. W.D. 1992); Brundige v. Boehringer Ingelheim, 812 S.W.2d 200, 202 (Mo. App. 1991). Claimant must prove "a direct causal connection between the conditions under which the work is performed and the occupational disease." Webber v. Chrysler Corp., 826 S.W.2d 51, 54 (Mo. App. 1992); Sellers, 752 S.W.2d at 416; Estes v. Noranda Aluminum, Inc., 574 S.W.2d 34, 38 (Mo. App. 1978). However, such conditions need not be the sole cause of the occupational disease, so long as they are a major contributing factor to the disease. Hayes, 818 S.W.2d at 299; Sheehan v. Springfield Seed \& Floral, 733 S.W.2d 795, 797-8 (Mo. App. 1987). A single medical opinion will support a finding of compensability even where the causes of the disease are indeterminate. Dawson, 885 S.W.2d at 716; Sellers, 776 S.W.2d at 504; Sheehan, 733 S.W.2d at 797. The opinion may be based on a doctor's written report alone. Prater v. Thorngate, Ltd., 761 S.W.2d 226, 230 (Mo. App. 1988). Where the opinions of medical experts are in conflict, the fact-finding body determines whose opinion is the most credible. Hawkins v. Emerson Electric Co., 676 S.W.2d 872, 877 (Mo. App. 1984). Where there are conflicting medical opinions, the fact finder may reject all or part of one party's expert testimony which it does not consider credible and accept as true the contrary testimony given by the other litigant's expert. George v. Shop 'N Save Warehouse Foods, Inc., 855 S.W.2d 460, 462 (Mo. App. E.D. 1993); Webber, 826 S.W.2d at 54; Hutchinson v. Tri-State Motor Transit Co., 721 S.W.2d 158, 163 (Mo. App. 1986).
Although workers' compensation is a creature of statute, many common law pleading principles apply, such as the rule that whenever a claim asserted in an amended pleading arose out of the conduct, transaction or occurrence set forth or attempted to be set forth in the original pleading, the amendment relates back to the date of the original pleading. Holaus v. William J. Zickell Co., 958 S.W.2d 72 (Mo. App. E.D. 1997).
The test of whether an amended claim relates back to the date of filing of the original claim is whether the
amendment amplifies the claim in the original pleading or sets up a new cause of action. Ford v. American Break Shoe Company, 252 S.W.2d 649 (Mo. App. 1952).
Our courts have repeatedly held that procedural rights are considered as subsidiary and substantive rights are to be enforced at the sacrifice of procedural formality. If a second claim filed is for the same injury, the second claim is tantamount in legal effect to the filing of an amended claim which supersedes the original claim. Silas v. ACF Industries, Inc., 440 S.W.2d 189 (Mo. App. 1969).