This systematic review aims to summarise the evidence from studies that examined morphometric alterations of the deep neck muscles using diagnostic imaging (ultrasound imaging, magnetic resonance imaging, and computed tomography) in patients diagnosed with primary headache disorders (PHD). No previous reviews have focused on documenting morphometric changes in this population. We searched five databases (up to 12 November 2022) to identify the studies. The risk of bias (RoB) was assessed using the Quality in Prognostic Studies (QUIPS) tool and the overall quality of the evidence was assessed using The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. A total of 1246 studies were screened and five were finally included; most were at high RoB, and the overall level of confidence in results was very low. Only two studies showed a significant association between morphometric alterations of the deep neck muscles and PHD (p < 0.001); nevertheless, their RoB was high. Contradictory and mixed results were obtained. The overall evidence did not show a clear association between morphometric alterations of the deep neck muscles in patients diagnosed with PHD. However, due to the limited number of studies and low confidence in the evidence, it is necessary to carry out more studies, with higher methodological quality to better answer our question.

Background and objectives: Chronic tension-type headache (TTH) is the type of headache with the highest prevalence. The involvement of musculoskeletal structures in TTH is supported by evidence in the scientific literature. Among these, deep cervical muscle strength appears to be related to the function of the cervical spine and the clinical characteristics of TTH. This study aimed to correlate anatomical, functional, and psychological variables in patients with TTH. Materials and methods: An observational descriptive study was carried out with 22 participants diagnosed with TTH for at least six months. The characteristics of headaches, including ultrasound-based deep neck flexor and extensor muscle thickness, range of motion (ROM), and pressure pain threshold (PPT), were recorded. We also conducted the Pain Vigilance and Awareness Questionnaire (PVAQ) and the Craniocervical Flexion Test (CCFT). Results: Moderate-large negative correlations were found between the PVAQ and the muscle thickness of right deep flexors contracted (r = -0.52; p = 0.01), left multifidus contracted (r = -0.44; p = 0.04), right multifidus at rest (r = -0.48; p = 0.02), and right multifidus contracted (r = -0.45; p = 0.04). Moderate-large positive correlations were found between the CCFT score and the left cervical rotation ROM (r = 0.53; p = 0.01), right cervical rotation ROM (r = 0.48; p = 0.03), muscle thickness of left multifidus contracted (r = 0.50; p = 0.02), and muscle thickness of right multifidus at rest (r = 0.51; p = 0.02). The muscle thickness of the contracted right deep cervical flexors showed a moderate negative correlation with headache intensity (r = -0.464; p = 0.03). No correlations were found between PPT and the rest of the variables analyzed. Conclusions: In patients with TTH, a higher thickness of deep cervical muscles was associated with higher ROM and higher scores in the CCFT. In turn, the thickness of deep cervical muscles showed negative correlations with pain hypervigilance and headache intensity. These results contribute to a better understanding of the physical and psychosocial factors contributing to the development of TTH, which is useful for implementing appropriate prevention and treatment measures.