Early thinking palliative care for people with Parkinson's disease: A thematic synthesis based on a systematic mixed-methods review.

Temporomandibular disorders (TMD) comprise heterogeneous conditions involving pain and/or dysfunction of the masticatory muscles, temporomandibular joints (TMJs), and associated structures. While TMD ranks as the second most prevalent musculoskeletal condition after low back pain, with a global prevalence exceeding 30% among adults, clinically relevant painful TMD affects approximately 10% of the population. TMD imposes a substantial societal and economic burden, with annual US healthcare expenditures estimated at $4 billion, nearly double that of individuals without TMD. Much of this financial burden is concentrated among a small subset of patients, suggesting important heterogeneity across TMD subtypes. TMD is also associated with lower quality of life, greater psychological distress, and functional limitations. Multiple comorbidities frequently coexist with TMD, many of which fall under the umbrella of chronic overlapping pain conditions (COPCs). Evidence from cross-sectional and case–control studies shows that adults with TMD exhibit a higher prevalence of migraine, headache, fibromyalgia, gastrointestinal (GI) disorders, chronic fatigue syndrome, interstitial cystitis, among others, compared with those without TMD. Adults with TMD present with significantly higher psychological distress, including anxiety, depression, and pain catastrophizing. Higher number of comorbidities has also been correlated with greater TMD pain intensity and chronicity. Multiple comorbidities also increase TMD risk. For example, findings from the OPPERA study and others indicate that individuals with widespread pain, multiple painful comorbidities, nonspecific orofacial symptoms, and psychosocial distress are at higher risk of developing TMD than those without such conditions. Moreover, individuals with TMD have 6-fold higher odds of developing additional medical comorbidities after TMD onset. Despite these associations, different TMD subtypes may exhibit distinct comorbidity patterns. To date, few studies have investigated comorbidity patterns by subtype, and most have focused on painful TMD. For example, Dahan et al. reported significantly higher prevalence of self-reported migraine and chronic fatigue syndrome among individuals with myofascial TMD compared with those without myofascial pain. Similarly, in patients with muscular TMD subtypes, diagnoses of migraine and chronic fatigue syndrome were associated with higher pain intensity and duration, an effect not observed in articular TMD. Gonçalves et al. observed increased odds of headache in painful myofascial TMD but not in articular subtypes. However, these studies were limited by small sample sizes and specific clinical populations.