Article 84 of the European Patent Convention (EPC) requires that the claims of a European patent application “shall define the matter for which protection is sought” and “shall be clear and concise and be supported by the description.”[i] To assist practitioners and patent examiners, the European Patent Office (EPO) provides patent examination guidelines interpreting the EPC. Recently, the EPO updated these guidelines, including Guideline F-IV 4.3, which interprets the requirements of EPC Article 84. New Guideline F-IV 4.3 provides strict description (i.e., specification and drawings) amendment requirements by providing that “[a]ny inconsistency between the description and the claims must be avoided if it could throw doubt on the subject-matter for which protection is sought and therefore render the claim unclear or unsupported under Art. 84,” such as where “[p]art of the description and/or drawings is inconsistent with the subject-matter for which protection is sought.”[ii] This may occur where parts of the description are not encompassed by the wording of the claims or are inconsistent therewith, such as may reasonably result from making amendments to the claims that are narrower than the full scope of the original description. In such situations, Guideline F-IV 4.3 specifically instructs that “[t]he applicant must remove any inconsistencies by amending the description either by deleting the inconsistent embodiments or marking them as not falling within the subject-matter for which protection is sought.”[iii]

In the U.S., a determination of infringement begins with the court construing the meaning of the claims asserted.[iv] As part of construing the claims, the doctrine of prosecution history estoppel “requires that the claims of a patent be interpreted in light of the proceedings in the PTO during the application process”[v] and “preclud[es] a patentee from regaining, through litigation, coverage of subject matter relinquished during prosecution of the application for the patent.”[vi] Estoppel may arise, for instance, from arguments and representations made to obtain allowance of a patent even without any claim amendments,[vii] and estoppel resulting from arguments and representations regarding one claim or application may limit the scope of related patents.[viii] To this end, the Federal Circuit considers a patentee’s representation made to a foreign patent office if the representation is (a) a “blatant admission;”;[ix] (b) “made in an official proceeding in which the patentee had every incentive to exercise care in characterizing the scope of its invention;”;[x] (c) “consistent with the claims and the invention described in the specification” of the U.S. application; and (d) “relevant and not related to unique aspects of foreign patent law.”[xi]

Based on the foregoing, an interesting question arises: Could a requisite description amendment made in a European application limit the scope of a counterpart U.S. application during litigation in the U.S.? While no court in the U.S. has yet faced this question, such a situation is likely forthcoming. For example, many entities elect to file counterpart applications in Europe and the U.S., and it is not unheard of for such applications to issue with claims that are identical or otherwise commensurate in scope. And it is foreseeable that the European patent could issue with a description that is different from (namely, narrower than) the specification of the counterpart U.S. patent, such as might result if the claims of each were similarly narrowed during prosecution and the EPO required a description amendment. In such a situation, prongs (b) and (c) are likely established with little effort, and the court need only determine whether the representation satisfies prong (a) as a “blatant admission” and prong (d) by not being related to unique aspects of European patent law.

As for prong (a), it is entirely possible that a court could interpret a description amendment as a “blatant admission” because such a description amendment, at least implicitly, indicates the patentee’s position on the scope of the claims and is relevant to the scope of the claims of the counterpart U.S. patent.[xii] Prong (d), on the other hand, is a bit murkier. The EPC description amendment requirement is admittedly “related to unique aspects of foreign patent law” because no equivalent requirement is found in the U.S. patent laws. Notwithstanding, it is possible that a court could reframe the analysis and find that because the description amendment requirement relates to issues of claim scope, a patentee’s compliance therewith is not “related to unique aspects of foreign patent law,” thereby satisfying prong (d) and permitting the patentee’s description amendment to be considered in construing the claims of the counterpart U.S. patent.[xiii] As may now be appreciated, the recent European description amendment requirements may invoke important issues for careful consideration by U.S. practitioners. As a result, applicants and practitioners should be mindful when drafting patent applications to avoid inconsistencies between the description and the claims. Relatedly, applicants and practitioners should be cautious and exercise due care when prosecuting a European patent application, especially if required to make a description amendment. Finally, applicants and practitioners should be cognizant that representations made to foreign patent offices, including responses to EPC description amendment requirements, may be able to be used against them during U.S. litigation.

[i] EPC Art. 84, available at

[ii] EPO Guideline for Examination F-IV 4.3, available at

[iii] Id.

[iv] Cybor Corp. v. FAS Techs., Inc., 138 F.3d 1448, 1454 (Fed. Cir. 1998) (en banc).

[v] Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722, 733 (2002).

[vi] Wang Labs., Inc. v. Mitsubishi Elecs. Am., Inc., 103 F.3d 1571, 1577–78 (Fed. Cir. 1997).

[vii] Andersen Corp. v. Fiber Composites LLC, 474 F.3d 1361 (Fed. Cir. 2007).

[viii] Southwall Techs., Inc. v. Cardinal IG Co., 54 F.3d 1570 (Fed. Cir. 1995).

[ix] See Gillette Co. v. Energizer Holdings, Inc., 405 F.3d 1367, 1374 (Fed. Cir. 2005) (considering a patentee’s arguments before the EPO and concluding that a “blatant admission by this same defendant before the EPO clearly supports” the court’s construction).

[x] See Microsoft Corp. v. Multi–Tech Sys., Inc., 357 F.3d 1340, 1350 (Fed. Cir. 2004) (noting that “any statement of the patentee in the prosecution of a related application as to the scope of the invention would be relevant to claim construction, and the relevance of the statement made in this instance is enhanced by the fact that it was made in an official proceeding in which the patentee had every incentive to exercise care in characterizing the scope of its invention”).

[xi] Apple Inc. v. Motorola, Inc., 757 F.3d 1286, 1312-13 (Fed. Cir. 2014), overruled on other grounds by Williamson v. Citrix Online, LLC, 792 F.3d 1339 (Fed. Cir. 2015).

[xii] Cf. Gillette, 405 F.3d at 1374 (Fed. Cir. 2005) (holding that a patentee’s arguments before the EPO regarding claim scope could be used in construing claims of U.S. patent because such arguments were a “blatant admission” as to claim scope).

[xiii] Cf. Abtox, Inc. v. Exitron Corp., 131 F.3d 1009, 1010 (Fed. Cir. 1997) (holding it improper to construe similar claim terms differently in one patent than another, given a common ancestry).