Chapter 50: Disorders of Musculoskeletal Function – Rheumatic

Disorders of Musculoskeletal Function – Rheumatic explores the wide spectrum of rheumatic disorders, ranging from localized joint conditions to complex, multisystem systemic autoimmune diseases. A significant focus is placed on Rheumatoid Arthritis (RA), a chronic inflammatory disorder where an aberrant immune response leads to the formation of destructive vascular granulation tissue known as pannus, resulting in bilateral, symmetric joint involvement and eventual deformity, such as swan neck or boutonnière deformities. The discussion extends to Systemic Lupus Erythematosus (SLE), frequently termed the "great imitator," which involves B-cell hyperreactivity, the creation of autoantibodies (like anti-DNA and ANA), and widespread immune complex damage affecting systems like the kidneys, CNS, and skin (classic butterfly rash). Other systemic disorders examined include Systemic Sclerosis (Scleroderma), characterized by excessive collagen deposition and fibrosis, particularly the CREST syndrome variant, and chronic inflammatory myopathies such as Polymyositis and Dermatomyositis. The text also delves into Seronegative Spondyloarthropathies (SpA), which are defined by the absence of rheumatoid factor and primarily affect the axial skeleton at the points where ligaments and tendons insert into bone, showing a strong link to the HLA-B27 antigen. This group includes Ankylosing Spondylitis (AS)—a prototype leading to progressive spinal fusion and stiffness—as well as Reactive Arthritis and Psoriatic Arthritis. Separately, the chapter details Osteoarthritis (OA), the most common form of arthritis and a leading cause of disability, resulting from the progressive degeneration and loss of articular cartilage, leading to bony outgrowths called osteophytes. Finally, Crystal-Induced Arthropathies are covered, specifically Gout, which results from hyperuricemia (elevated uric acid) and subsequent deposition of monosodium urate crystals, often in peripheral joints, leading to severe inflammatory attacks and chronic tophi formation. The chapter concludes by addressing the unique presentations and challenges of these rheumatic conditions in pediatric patients (Juvenile Idiopathic Arthritis) and older adults, where conditions like Polymyalgia Rheumatica often present.