The similar names of polymyalgia rheumatica (PMR) and fibromyalgia (FM), coupled with shared generalized muscle pain, often cause confusion. Both conditions profoundly impact quality of life through chronic discomfort and stiffness, yet they arise from fundamentally different biological processes. Understanding these distinct mechanisms, symptom patterns, and treatment modalities is necessary for accurate diagnosis and effective long-term care.
The Underlying Nature of Each Condition
Polymyalgia rheumatica is an inflammatory rheumatic disease driven by systemic inflammation throughout the body. It is considered immune-mediated, where the immune system mistakenly targets and attacks tissues, specifically the synovium and bursae surrounding large joints. This inflammatory process is typically seen in older adults, with the average age of onset being around 70 years. The systemic nature of PMR is often accompanied by objective laboratory evidence of inflammation.
Fibromyalgia, by contrast, is not considered an inflammatory or autoimmune disorder. Instead, it is defined as a chronic centralized pain disorder, representing an issue with how the central nervous system processes pain signals. This involves central sensitization, where the brain and spinal cord become highly sensitive to pain, amplifying sensations that would normally not be painful. The condition affects a much broader age range than PMR and is significantly more common in women.
How Pain and Symptoms Present Differently
The pain and stiffness associated with polymyalgia rheumatica are highly localized, concentrating primarily in the shoulder and pelvic girdles. Discomfort is most noticeable in the muscles of the neck, shoulders, upper arms, hips, and thighs on both sides of the body. A defining characteristic of PMR is severe morning stiffness that can last for hours, making basic tasks difficult. PMR often presents with systemic signs of illness, such as a low-grade fever, general malaise, loss of appetite, and unintended weight loss, which result from the underlying inflammation.
Fibromyalgia pain is characterized by widespread, chronic pain present in all four quadrants of the body for a minimum of three months. Patients often describe the pain as a deep ache, burning, or throbbing sensation that is relentless. While PMR is marked by stiffness, FM is noted for specific tender points, areas of localized tenderness upon light touch. Fatigue in FM is pervasive, frequently accompanied by non-restorative sleep, irritable bowel syndrome, and cognitive difficulties often referred to as “fibro fog.”
Distinguishing Factors in Diagnosis
The diagnostic process for polymyalgia rheumatica relies heavily on objective laboratory evidence of inflammation. Physicians order blood tests to measure the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), which are typically highly elevated in PMR patients. The combination of specific symptoms—bilateral pain and stiffness in the shoulder and hip areas in a patient over 50—and these elevated markers strongly indicates a PMR diagnosis. A rapid and dramatic response to a low-dose course of corticosteroids can also be used as a therapeutic test.
Fibromyalgia diagnosis is a diagnosis of exclusion, meaning other conditions must be ruled out before confirmation. Since it is not an inflammatory disorder, laboratory inflammatory markers (ESR and CRP) are characteristically normal or only mildly elevated, which differentiates it from PMR. Diagnosis is based on clinical criteria, specifically assessing the Widespread Pain Index (WPI) and the Symptom Severity (SS) scale. The WPI quantifies the number of painful body areas, while the SS scale measures the severity of fatigue, unrefreshing sleep, and cognitive symptoms.
Contrasting Treatment and Management
Treatment for polymyalgia rheumatica aims directly at resolving the underlying inflammation. The standard and most effective treatment is a course of oral corticosteroids, such as prednisone. Patients often experience a quick reduction in pain and stiffness once treatment begins, sometimes within days, which serves as a confirming diagnostic sign. Management involves a carefully monitored, gradually tapered dose of the steroid over one to two years to prevent relapse and minimize side effects.
Fibromyalgia management is multimodal because there is no single inflammatory process to target. Treatment focuses on modulating the sensitized nervous system and managing the diverse array of symptoms. Non-pharmacological interventions are foundational, including aerobic exercise, cognitive behavioral therapy (CBT), and strict sleep hygiene practices. Specific medications are used to address pain processing and sleep disturbances, such as certain anticonvulsants (like pregabalin), selective serotonin and norepinephrine reuptake inhibitors (SNRIs), and tricyclic antidepressants.