To study and summarize the clinical features of hypophosphatemia osteomalacia (HO) misdiagnosed as spondyloarthritis (SpA), aiming to analyze the reasons of misdiagnosis and improve the prognosis of such patients.
A total of 26 cases of HO misdiagnosed as SpA were selected. Clinical features, laboratory tests, and image presentations were analyzed. Related literatures were reviewed.
(1) Clinical characters: 26 patients were included (12 males and 14 females) with a median age of 38 years (range 20-60). The mean disease duration was 3.2 years (range 0.75 to 10 years). Of all the patients, 15 were diagnosed as tumor-induced HO, 4 were long-term oral adefovir dipivoxil-related HO, 3 were associated with Fanconi syndrome, 2 were related to hyperparathyroidism, while 2 were Sjogren's syndrome complicated with renal tubular acidosis. All of the 26 patients presented with low back pain including 15 with night pain. The time of morning stiffness was about 30 minutes. Non-steroidal anti-inflammatory drugs were given to each patient whereas with poor efficacy, neither did other agents work well, such as glucocorticoids, disease modifying anti-rheumatic drugs and biologics. (2) LABORATORY FINDINGS: the platelet count and inflammatory markers such as erythrocyte sedimentation rate, C-reactive protein (CRP) were usually normal. The level of serum calcium was normal or slightly lower, nevertheless, all patients had hypophosphatemia and increased level of alkaline phosphatase (ALP). Patients with adefovir dipivoxil-related HO, Fanconi syndrome or Sjogren's syndrome complicated with renal tubular acidosis were characterized by hypokalemia, hyperchloremia and alkaline urine. Patients with hyperparathyroidism had elevated parathyroid hormone (PTH). Positive antinuclear antibodies (ANA) (titer ≥ 1: 320), anti-SSA/SSB antibodies were found in patients with Sjogren's syndrome. (3) Radiographic features: sacroiliac joint lesions were found in X-ray, CT, positron emission tomography (PET-CT) or MRI, however the lesions in sacrum or ilium were predominant rather than in joints. Abnormal bone imaging in ribs, long bones and soft tissues in addition to joints could be detected by bone scintigraphy.
HO is not uncommon in daily practice. Besides SpA, other diseases should be considered in the setting of low-back pain and diseased sacroiliac joints. Comprehensive screening of bone metabolic parameters contributes to the timely diagnosis of HO.