43 year old HIV positive, type I diabetic female (on lopinavir-ritonavir, efavirenz; last CD4 count 942; negative viral load), presented to Emergency Department (ED) with lower back pain radiating bilaterally to buttocks for one week. Physical examination revealed paraspinal tenderness, intact rectal tone and saddle sensation, no motor weakness. Magnetic Resonance Imaging (MRI) of lumbosacral spine 2 days prior showed chronic spinal stenosis with sacral soft tissue edema. Laboratory work up revealed blood glucose 680 mg/dl, ketonuria, Erythrocyte Sedimentation Rate 100 mm/hr, C Reactive Protein 28 mg/dl and she was hospitalized for diabetic ketoacidosis. Chest x-ray on day 2 showed bilateral parenchymal densities with Computed Tomography (CT) scan revealing pulmonary nodular consolidation. She was empirically started on vancomycin and zosyn. On day 3, blood culture grew Methicillin Resistant Staphylococcus Aureus. Other work up – Pneumocystis jiroveci Polymerase Chain Reaction, Herpes Simplex culture, Cytomegalovirus culture from bronchoalveolar lavage, were negative. Transthoracic Echocardiogram negative for vegetations with no other infection source identified. Patient gradually recovered getting discharged on oral linezolid. However, she still had lower back pain. MRI now showed abnormal iliac bone marrow signals with epidural edema at the L4-L5 level causing severe canal stenosis. Antibiotic was now switched to intravenous vancomycin. Interestingly, biopsy of right sacroiliac bone revealed Staphylococcus aureus with blood cultures now negative. Intravenous vancomycin was continued to complete twelve total weeks of antibiotics.
Infectious sacroiliitis forms less than two percent of infectious arthritis. Risk factors are intravenous drug use, diabetes, immunosuppression, trauma, focus of infection elsewhere. Commonest presenting symptom is unilateral lumbogluteal back pain. Most cases are caused by Staphylococcus aureus with Pseudomonas aeruginosa being commonest in intravenous drug users. Since x-rays take up to two weeks to demonstrate bone changes, MRI is the gold standard investigation. CT scan may not be diagnostic early on but is used to guide bone marrow aspiration. Intravenous antibiotics empirically directed against Staphylococcus aureus are mainstay of treatment. There is no consensus on duration so treatment must be individualized. British guidelines recommend intravenous antibiotics for three weeks with 6 to 12 weeks of oral antibiotics.
Our case illustrates the need to be aware of uncommon conditions like infectious sacroiliitis with an increasing prevalence of medically controlled HIV positive individuals. This treatable condition must be considered in any patient with risk factors and unexplainable lower back pain to ensure timely management.