Differentials
Giant cell arteritis (GCA)
SIGNS / SYMPTOMS
New-onset unilateral headache, jaw claudication associated with chewing tough foods, diffuse mandibular discomfort, dental discomfort, sinus pain and pressure, and/or tongue pain are associated with GCA. Blindness, diplopia, or blurry vision and an abnormally thickened, tender, erythematous, or nodular temporal artery are also found.[9]
INVESTIGATIONS
A positive temporal artery biopsy showing a granulomatous vasculitis confirms the diagnosis of GCA; however, results may be positive in PMR patients without GCA symptoms.
Early rheumatoid arthritis (RA)
SIGNS / SYMPTOMS
Presentation may be very similar to PMR; however, the absence of a prompt response to low-dose corticosteroids distinguishes the two. The peripheral musculoskeletal symptoms of early RA do not respond rapidly.[4] Some patients with RA will respond to 10 to 20 mg of prednisone.
INVESTIGATIONS
Elevated rheumatoid factor and persistently elevated plasma viscosity.[35] Positive anti-CCP antibody assays.[1] Anti-CCP assays were 61.4% sensitive and 100% specific for the diagnosis of late-onset RA.[36]
Repeat x-ray of hands, delayed for months after the initial test, is performed to assess other affected joint damage.[4]
Hypothyroidism
SIGNS / SYMPTOMS
May show similar signs of muscle and joint pain, weakness in the extremities, and fatigue; however, delayed relaxation of deep tendon reflexes (a rare finding) is strongly suggestive of hypothyroidism.[4]
INVESTIGATIONS
An elevated TSH helps to differentiate hypothyroidism.[4] Creatine phosphokinase may also be elevated.
Fibromyalgia
Paraneoplastic syndrome
SIGNS / SYMPTOMS
May present with constitutional symptoms and proximal muscle pain easily confused with the shoulder and hip girdle stiffness found in PMR. Paraneoplastic syndrome symptoms usually do not respond to low-dose corticosteroid treatment. A thorough tumor workup should be reserved for those unresponsive to low-dose glucocorticoid therapy. Removal of the tumor leads to a resolution of symptoms.[5]
The Lambert-Eaton syndrome, a paraneoplastic condition associated with small-cell lung cancer, may cause proximal weakness that improves later in the day, a feature similar to the symptoms of PMR.
INVESTIGATIONS
Tumor screening includes routine baseline tests including a CXR, a CBC, a chemistry panel, and urinalysis. Age-appropriate cancer screening tests should also be performed (i.e., fecal occult blood testing, colonoscopy, mammogram). Additional specialized testing should be directed by the history, the exam findings, and any abnormalities found on the routine CXR and laboratory tests.
Polymyositis
SIGNS / SYMPTOMS
Symmetrical weakness of shoulder and pelvic girdles.[4]
INVESTIGATIONS
Elevated muscle enzyme levels (i.e., creatine phosphokinase) often with a positive antinuclear antibody titer. Characteristic changes in electromyography associated with polymyositis include increased needle insertional activity, spontaneous fibrillations, low-amplitude, short-duration polyphasic motor potentials, and complex repetitive discharges. Diagnosis is confirmed with muscle biopsy, indicating immune cell infiltration and destruction of muscle fibers.[4]
Overuse bursitis/tendonitis
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