Elderly-onset rheumatoid arthritis (EORA) and polymyalgia rheumatica (PMR) are among the most frequent inflammatory rheumatic diseases in patients over 50, yet their clinical differentiation, particularly when EORA presents with polymyalgic onset, poses a common diagnostic challenge. This systematic review aimed to identify the pathophysiological, clinical, imaging and treatment-response features that distinguish EORA from PMR. MEDLINE, CENTRAL and Scopus (inception to January 2026), with supplementary searches of LILACS, Google Scholar and trial registries (June 2026) were searched, including studies that compared EORA with PMR or reported separately extractable data for both; risk of bias was appraised with design-specific tools and the evidence weighted accordingly. Seventy-one studies across four domains were included: pathophysiology (22 studies), clinical presentation and final diagnosis at follow-up (24 studies), imaging (21 studies), and treatment response (4 studies). Genetically, in one low risk of bias study that stratified EORA by rheumatoid factor status, PMR and seronegative EORA shared HLA-DRB1*13/*14 associations, a pattern distinct from the shared epitope-driven susceptibility of seropositive RA. However, divergent metabolomic signatures suggest different downstream inflammatory mechanisms. An exploratory random-effects meta-analysis yielded a pooled PMR-to-RA reclassification rate of 7% (95% CI 4-12%; 9 studies), narrowing to 4% (95% CI 2-7%) in methodologically robust studies, though rates of reclassification to RA were considerably higher (up to 20%) when patients with undifferentiated polymyalgic presentations were included. Peripheral arthritis occurred in 28% of PMR patients (95% CI 20-35%; 6 studies), with a significant difference between baseline prevalence (21%) and cumulative incidence over follow-up (34%) on subgroup meta-analysis (p = 0.026), and was characteristically transient and glucocorticoid-responsive, whereas persistent synovitis involving wrists and small joints was associated with reclassification to RA. On imaging, evidence from low-to-moderate risk of bias, ultrasound studies showed that shoulder findings overlapped substantially between conditions, whereas bilateral hip synovitis was significantly more frequent in PMR (47% vs 0% in RA), suggesting the hip as a stronger proximal informative site. However, distal joint synovitis demonstrated the highest discriminatory value, with the presence of at least one among RF positivity, hand grey-scale ≥2, or hand power Doppler ≥1 achieving 89% sensitivity and 93% specificity for EORA identification. This review highlights that the distinction between EORA and PMR cannot be reliably established at a single time point and that longitudinal reassessment integrating clinical, serological, and imaging findings remains essential for the differential diagnosis. However, the evidence is limited by clinical and methodological heterogeneity and the predominance of observational designs.

GIM/FP/GP: [Formula: see text] Rheumatology: [Formula: see text].

Whole-body magnetic resonance imaging (WBMRI) has emerged as the primary imaging tool for multifocal inflammatory and infectious musculoskeletal diseases. By extending coverage from the vertex to the toes in a single, radiation-free examination, WBMRI enables the detection of clinically occult lesions, disease-specific pattern recognition across bone marrow, joints, entheses, and muscles, and objective monitoring of disease activity and treatment response. This review describes the WBMRI findings-with detailed imaging features and distribution patterns-in chronic nonbacterial osteitis, SAPHO syndrome, seronegative spondyloarthritis, rheumatoid arthritis, juvenile idiopathic arthritis, polymyalgia rheumatica, idiopathic inflammatory myopathies, and fever of unknown origin, with emphasis on validated quantitative scoring tools, disease-specific acquisition protocols, and structured reporting strategies for the practicing radiologist. WBMRI provides unique clinical value by mapping total lesion burden, supporting differential diagnosis, identifying biopsy targets, and tracking treatment response. Disease-specific protocols-tailored to the pathophysiological target of each condition-are essential for maximizing diagnostic yield. Quantitative scoring tools and advanced MRI sequences may improve the characterization of disease burden and longitudinal assessment.

A man in his late 70s presented with 6-week bilateral shoulder and hip girdle pain, morning stiffness and significant weight loss. Although polymyalgia rheumatica was initially suspected, red flag weight loss prompted referral through the 2 week-wait cancer pathway with parallel laboratory and imaging assessment.Markedly elevated creatine kinase (>5000 U/L), proximal weakness and subtle cutaneous features raised suspicion of dermatomyositis. A CT scan then demonstrated extensive intra-abdominal and right inguinal lymphadenopathy, initially suggesting lymphoma and prompting haematology referral. Ultrasound-guided lymph node biopsy unexpectedly confirmed metastatic melanoma.Subsequent skin and nail examination identified a pigmented right great toe lesion, previously attributed to trauma, consistent with the primary acral melanoma. The overall picture was paraneoplastic dermatomyositis presenting as a polymyalgia-like syndrome. Corticosteroids and B-Raf proto-oncogene, serine/threonine kinase (BRAF)/mitogen-activated protein kinase (MEK) targeted therapy were followed by resolution of muscle symptoms and radiological response.