Spondylodiscitis is an infection of an intervertebral disc and the vertebrae. Its incidence is on the rise in recent years. The causative microorganism in most adult patients is Staphylococcus aureus. To date, Streptococcus species have had little relevance as causative agents of vertebral osteomyelitis. However, the number of cases caused by these microorganisms has increased in recent years.1 We report the case of a patient with spondylodiscitis caused by Streptococcus mitis.

The patient was a 49-year-old man, an ex-smoker, with nothing else remarkable in his clinical history. He presented with a 4-week history of low back pain with inflammatory features and pain that radiated down his left leg. He did not have associated fever or metabolic syndrome. There was no evidence of skin lesions, either, and he did not consume farmhouse dairy products. He had not undergone any dental procedures in the preceding 2 years. Notable findings in the results of laboratory tests were the absence of leukocytosis in the complete blood count and a normal differential leucocyte count, but elevation of acute-phase reactants was detected (erythrocyte sedimentation rate [ESR], 80mm; C-reactive protein [CRP], 42mg/L). Serological tests for human immunodeficiency virus and Brucella were negative, as was the tuberculin skin test. A radiograph of the lumbar spine revealed a slight irregularity in the vertebral endplate below L5. Magnetic resonance imaging of the lumbosacral spine disclosed signs compatible with spondylodiscitis involving L5–S1. Blood cultures were negative. A transthoracic echocardiogram showed no evidence of endocarditis. Finally, a biopsy and fine-needle aspiration cytology were performed, both under computed tomography (CT) guidance. Bacterial culture yielded colonies of S. mitis that were sensitive to all the different classes of antibiotics except penicillin. Four hours after the vertebral biopsy, a blood sample was again obtained for culture, in which S. mitis was also isolated. Treatment consisted of intravenous ceftriaxone for 3 weeks, followed by another 3 weeks with oral levofloxacin. The patient responded well to the treatment, with resolution of the clinical signs and normalization of the acute-phase reactants.

To date, 7 cases of spondylodiscitis caused by S. mitis have been reported in the English-language literature1–3 (PubMed: Spondylodiscitis and S. mitis 1969–2015). S. mitis, which belongs to the group of viridans streptococcal species, forms part of the commensal flora of the mouth and nasal sinuses and is a rare cause of spondylodiscitis. Spondylodiscitis is uncommon in adults. The predisposing factors are diabetes mellitus, malnutrition, intravenous drug use, immunodeficiency, neoplasms, prolonged glucocorticoid therapy, chronic kidney disease and cirrhosis. It usually presents with inflammatory back pain, which can be accompanied by fever and clinical signs of a systemic disorder.2 In contrast to spondylodiscitis caused by S. aureus and by streptococci from a group other than viridans, that attributed to viridans streptococci has a more subacute course, with less systemic involvement. For this reason, the diagnostic delay is usually longer. The majority of the patients with infection caused by this microorganism present with infective endocarditis, as well. Thus, performance of echocardiography is indispensable in these patients.1–5 Laboratory tests reveal leukocytosis and neutrophilia, as well as elevated acute-phase reactants (ESR, CRP). Blood cultures are essential for the microbiological diagnosis and avoid the need for more invasive procedures. Imaging studies (plain radiography, CT or nuclear magnetic resonance) are performed to exclude other diseases and to identify signs suggestive of spondylodiscitis, as well as to rule out its complications. The definitive diagnosis requires the isolation of the causative pathogen, either in blood cultures or a biopsy. The latter can be percutaneous, and is generally CT-guided or open.6 Blood cultures performed during the first few hours after the biopsy have been reported to be more sensitive and, thus, are worthwhile as they can confirm that the infection was caused by the microorganism isolated in the biopsy specimen and is not the result of contamination.7