Polymyalgia rheumatica: pitfalls in diagnosis
- S Siebert, MB MRCP
- T M Lawson, PhD MRCP
- M H Wheeler, MD FRCS1
- J C Martin, MD MRCP2
- B D Williams, FRCP FRCPath
CASE HISTORIES
Case 1
For four months a woman aged 54 had experienced proximal myalgia and stiffness, worse in the morning. ESR was 92 mm/h and alkaline phosphatase (ALP) 436IU/L (normal < 115). Other liver function tests and tests of renal and thyroid function were normal. PMR was diagnosed and she was treated with prednisolone 15 mg daily. Symptoms resolved within 3 days.
One year later, on 7.5 mg prednisolone daily, she still complained of mild myalgia. ESR was 50 mm/h and ALP was 161 IU/L. Abdominal ultrasonography, arranged because of the persistently raised ALP, revealed a large mass in the left upper quadrant. A computed tomographic scan confirmed an 11 × 13 cm mass (Figure 1), which was removed at laparotomy and identified as a malignant adrenal cortical tumour. Postoperatively her symptoms resolved and steroids were withdrawn without recurrence of myalgia. The ESR and ALP became normal.
Figure 1
Computed tomographic scan of abdomen showing large left adrenal mass
Case 2
A woman aged 54 reported proximal muscle pain and stiffness, worse in the morning. No abnormalities were found on examination, and biochemical findings including creatine kinase and tests of renal, hepatic and thyroid function were likewise normal. There was evidence of a mild acute-phase response—ESR 15 mm/h, C-reactive protein 22 mg/L. PMR was diagnosed by her general practitioner, who prescribed prednisolone 15 mg daily. Symptoms improved greatly within 24 hours but recurred whenever the prednisolone was decreased below 15 mg daily. Further investigation showed a corrected calcium level of 2.7 mmol/L (normal < 2.6) and parathyroid hormone of 9.7 pmol/L (normal 0.9-5.4 pmol/L), results consistent with primary hyperparathyroidism. At parathyroidectomy she was found to have a parathyroid adenoma. Postoperatively her symptoms resolved within six months.
Case 3
A woman of 57 reported four months of shoulder and hip girdle pain and stiffness. No abnormalities were detected on physical examination. ESR was 70 mm/h and ALP was 161 IU/L; full blood count, calcium and muscle enzymes were normal. PMR was diagnosed, prednisolone 15 mg daily was prescribed and symptoms improved greatly within 48 hours.
Three months later, while taking 10 mg prednisolone daily, she developed severe left-sided headaches, jaw pain and scalp tenderness, associated with a rise in the ESR to 80 mm/h. Temporal arteritis was now diagnosed and the prednisolone dose was increased to 60 mg daily. Biopsy of the left temporal artery showed focal intimal fibrous proliferation but no active inflammation. Symptoms settled completely within two days and the ESR decreased to 42 mm/h within one month.
Three months later she was symptom-free on 30 mg prednisolone daily but her ESR and ALP remained raised at 60 mm/h and 191 IU/L respectively. An isotope bone scan showed widespread bony metastases, especially prominent in the skull, spine, femoral necks and sternum. Notably, there were several skull metastases in the left temporoparietal region, corresponding to the site of the previous pain and tenderness (Figure 2). A bone marrow aspirate revealed metastatic adenocarcinoma of unknown origin.
Figure 2
Isotope bone scan showing extensive bony metastases in skull and sternum
COMMENT
Many conditions can mimic PMR5,6, and features that should raise suspicion of an alternative diagnosis include young presenting age (< 65 years)2, normal inflammatory markers (though these are normal in 5-20% of patients with PMR7,8) and non-response to low-dose oral steroids. Another alerting feature is a persistently raised ALP. ALP is an acute-phase reactant9, and in one study of 74 patients with PMR it was raised in about one-third of cases10. However, on treatment with steroids the ALP became normal in every case within three weeks10. In both our patients with underlying malignancy the ALP remained high, and we suggest that such cases should be further investigated by abdominal ultrasound and isotope bone scan. While failure to respond to treatment with steroids should raise doubts about the diagnosis of PMR, a good response to steroids does not necessarily confirm the diagnosis. In all three of the cases reported here there was a good initial response to steroids.
Patients with suspected PMR should have baseline investigations including full blood count, ESR, C-reactive protein, renal, hepatic and thyroid function tests, calcium, creatine phosphokinase, serum electrophoresis and dipstick urinalysis. If there is nothing to suggest an alternative underlying diagnosis, treatment with low-dose oral steroids (prednisolone 10-20 mg daily) can be started. The presence of any atypical features should prompt more detailed investigation.
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