Differential Diagnosis for Polymyalgia Rheumatica (PMR)

Single Most Likely Diagnosis

• Polymyalgia Rheumatica (PMR): This is the most likely diagnosis given the symptoms of myalgia (muscle pain) and stiffness, particularly in the shoulders, neck, and hips, which are characteristic of PMR. The condition is more common in individuals over 50 years old.

Other Likely Diagnoses

• Giant Cell Arteritis (GCA): Often associated with PMR, GCA can present with similar symptoms and is a significant consideration due to its potential for serious complications, such as vision loss.
• Rheumatoid Arthritis (RA): Although RA typically affects the hands and feet more prominently, it can also cause widespread musculoskeletal pain and stiffness, making it a differential diagnosis for PMR.
• Osteoarthritis: While primarily a disease of the joints, osteoarthritis can cause significant pain and stiffness, especially in older adults, which might be confused with PMR symptoms.
• Fibromyalgia: Characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory, and mood issues, fibromyalgia could be considered in the differential diagnosis due to its overlapping symptoms with PMR.

Do Not Miss Diagnoses

• Infections (e.g., Endocarditis, Osteomyelitis): Although less common, infections can cause systemic symptoms including myalgias and must be considered to avoid missing a potentially life-threatening condition.
• Malignancy (e.g., Multiple Myeloma, Lymphoma): Certain cancers can present with musculoskeletal pain and stiffness, making them critical not to miss.
• Thyroid Disorders (Hypothyroidism): Hypothyroidism can cause muscle pain and stiffness, among other symptoms, and is important to diagnose due to its treatable nature.
• Drug-induced Myopathies: Certain medications can cause myopathy, which might mimic PMR symptoms.

Rare Diagnoses

• Inflammatory Myopathies (e.g., Dermatomyositis, Polymyositis): These are autoimmune conditions that cause muscle inflammation and weakness, which could be considered in the differential diagnosis, although they are less common.
• Sarcoidosis: A condition that can cause inflammation in various parts of the body, including the muscles, leading to symptoms that might be confused with PMR.
• Amyloidosis: A group of diseases that result from the abnormal accumulation of amyloid proteins, which can cause a wide range of symptoms, including muscle pain and weakness.

Each of these diagnoses requires careful consideration based on the patient's clinical presentation, laboratory findings, and imaging studies to accurately diagnose and treat polymyalgia rheumatica and its potential mimics.