“A study by Mills et al. (2020) found that of over 100 recent dog cases referred for problem behaviour, around one in three involved some kind of painful condition, with some caseloads showing a rate close to 80%.”

The cited paper exists and the claim's central numbers come from its published abstract. The abstract states that a review of the caseloads of 100 recent dog cases of several authors indicates that a conservative estimate of around a third of referred cases involve some form of painful condition, and in some instances the figure may be nearly 80%, and that the relationship is often complex but always logical. It adds that musculoskeletal but also painful gastro-intestinal and dermatological conditions are commonly recognised as significant to the animal's problem behaviour. The paper's own per-clinic figures are wider than the headline. Table 1 reports the proportion of behaviour cases where a painful condition was suspected as 68% (Bristol), 82% (Lincoln), 23% (Pennsylvania A), 29% (Pennsylvania B), 79% (Missouri/Illinois) and 28% (Barcelona), and the proportion of those cases with some form of confirmation of diagnosis as 79%, 56%, 61%, 79% and 72% across the first five sites. The authors describe the prevalence among the referral caseloads of several of the authors in recent years as ranging from 28 to 82%. The paper describes itself as a commentary rather than a formal epidemiological study. The authors write that in this commentary they present evidence from their own caseloads to illustrate the scale and nature of the issue, with a view to increasing awareness among veterinarians, non-veterinary behaviourists and owners. The introduction frames it as beginning with a brief review of 100 recent dog behaviour cases from several of the authors, and situates it against earlier reports of 5% prevalence (Voith) and later 12% in dogs and 19% in cats (Mills). An earlier unpublished 2013 review of one resident's case log at Lincoln returned 23% for dogs, which the authors describe as at the lower end of what is reported more recently across a wider geographic base. The authors are explicit that mechanism is often unknown. They state that while the actual mechanism underpinning the association between pain and problem behaviour may never be known in a given case, the relationship can be classified into one of four categories: the presenting complaint is a direct manifestation of pain, unidentified pain underpins secondary concerns, pain exacerbates one or more signs, or adjunctive behavioural signs are associated with pain. They argue that clinical abnormalities such as an unusual gait or unexplained behavioural signs should not be dismissed even when common within a breed, and that clinicians should err on the side of caution by carefully evaluating a patient's response to trial analgesia even where no specific physical lesion has been identified. The paper's figures are reported in the wider literature in the broader form. A 2025 Frontiers retrospective paper states that Mills et al. (2020) found 30 to 80% of patients referred for behavioural complaints had at least one underlying painful condition. The second cited source exists and is described broadly correctly by the post. The Camps, Amat and Manteca 2019 abstract states that medical problems can change behaviour directly or indirectly, that these problems represent a diagnostic challenge from a practical point of view, and that the most common sign of pain in animals is a change in behaviour. It states that thyroid hormones play an important role in behavioural control, that both hypothyroidism and hyperthyroidism have been related to behavioural changes, that the hypothyroidism relationship remains controversial, and that there are many neurological problems that could potentially change behaviour. The review also notes that the relation between sleep disorders and pain is poorly known in veterinary medicine and that the impact of behavioural problems on pain perception is completely unknown in dogs and cats.