A 70-year-old man presented with pain in his shoulders, low back, and thighs for 1 year. He had difficulties when changing clothes, taking a bath, and getting out of bed because all these body movements aggravated the pain. He also experienced morning stiffness for 1 hour. Although his weight decreased by 5 kg because of loss of appetite, he denied any nausea, diarrhea, depressed mood, fever, headache, visual disturbance, or jaw claudication. His medical history included diabetes mellitus with maintained hemoglobin A1c levels of <7% and dyslipidemia, for which he was taking 50 mg sitagliptin, 0.5 mg glimepiride, 750 mg metformin, and 2.5 mg rosuvastatin daily.
On physical examinations, he could neither raise his arms nor squat down because of pain, but his muscle strength was normal. None of his muscles and joints had redness, swelling, warmth, or tenderness. He had no tenderness on temporal or occipital arteries. Laboratory test results revealed mild normocytic anemia (13.0 g/dL of hemoglobin level and 87 fL of mean corpuscular volume) with a low level of serum iron (50 µg/dL). C-reactive protein (0.1 mg/dL), erythrocyte sedimentation rate (10 mm/h), and ferritin (86 ng/mL) levels were all normal.
All additional tests showed normal results, including adrenocorticotropic hormone and cortisol by an adrenocorticotropic hormone stimulation test, rheumatoid factor, anti-cyclic citrullinated peptide antibody, anti-nuclear antibody, and anti-neutrophil cytoplasmic antibody. Upper and lower endoscopies detected no abnormal findings. Ultrasound showed bilateral biceps tenosynovitis. Positron emission tomography (PET)/computed tomography (CT) revealed no malignancy or vasculitis, but 18F-fluorodeoxyglucose uptake was seen in the bilateral shoulders, hip joints, greater trochanter of femurs, and ischial tuberosities without any bone erosion (Figure). The pain did not improve after ceasing sitagliptin for more than 1 month. Although normal levels of C-reactive protein and erythrocyte sedimentation rate did not meet the criteria for polymyalgia rheumatica of the European League Against Rheumatism and the American College of Rheumatology in 2012, bilateral shoulder pain in patients who were aged >50 years, morning stiffness for >45 minutes, hip pain and limited range of movement, absence of rheumatoid factor and anti-cyclic citrullinated peptide antibody, and ultrasound findings in addition to PET/CT findings indicated a diagnosis of polymyalgia rheumatica. A prescription of 15 mg oral prednisolone improved his pain immediately, and this dosage was subsequently decreased to <5 mg over 1 year without relapse.
Polymyalgia rheumatica is a relatively common inflammatory disease in elderly individuals that mimics other conditions, including malignancy, infections, and rheumatic disorders.1 Although 7% to 20% of patients show low erythrocyte sedimentation rate in polymyalgia rheumatica, other diagnoses must be considered in patients with normal C-reactive protein in addition to low erythrocyte sedimentation rate for the rarity of such a condition.1 As one of the alternative disorders, drug-induced arthritis can be caused by antimicrobials, dipeptidyl peptidase-4 inhibitors, chemotherapeutics, retinoids, cytokines, and psychotropics.2 Because dipeptidyl peptidase-4 inhibitors, including sitagliptin, that our patient was taking can induce polyarthritis with normal inflammatory markers, these suspected drugs should be ceased for more than 1 month to exclude them as a causative factor. Another important differential diagnosis should be adrenal deficiency. It can cause muscle pain, arthralgia, low back pain, and limited range of movement,3 which are similar symptoms to polymyalgia rheumatica, with normal inflammatory markers. Moreover, because adrenal deficiency improves rapidly with low-dose steroid similar to polymyalgia rheumatica, a hormonal test should be done before trying treatment with prednisolone. Rheumatoid arthritis is a major mimic of polymyalgia rheumatica, and some patients show normal inflammatory markers. However, elderly-onset rheumatoid arthritis with polymyalgia rheumatic-like symptoms has a high level of C-reactive protein compared with those without polymyalgia rheumatica-like symptoms.4 PET/CT would play a significant role to exclude mimics and to detect polymyalgia rheumatica.
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-Shingo Suzuki, MD, PhD, Yuta Hirose, MD, Eriko Takeda, MD, Masatomi Ikusaka, MD, PhD
This article originally appeared in the July issue of The American Journal of Medicine.
