# Facet joint arthritis as the presenting symptom for culture-negative Aggregatibacter aphrophilus native valve endocarditis in a patient without known cardiac disease: a case report

## TL;DR

A rare case of Aggregatibacter aphrophilus endocarditis presented with arthritis in a patient without heart disease, highlighting the need for advanced diagnostic methods.

## Contribution

First reported case of A. aphrophilus causing facet joint arthritis and culture-negative endocarditis in a patient without cardiac disease.

## Key findings

- Facet joint arthritis was the initial symptom of A. aphrophilus endocarditis in a patient with no prior heart disease.
- Broad-range PCR on excised valve tissue confirmed A. aphrophilus despite negative blood cultures and initial tests.
- The patient's symptoms improved after aortic valve replacement, confirming the diagnosis and treatment effectiveness.

## Abstract

Aggregatibacter aphrophilus (A. aphrophilus) is a rare cause of infective endocarditis (IE), but is a recognized cause of culture-negative IE. The risk of developing IE is increased in patients with valvular disease or prosthetic valves. To our knowledge, A. aphrophilus has never previously been reported to cause lumbar facet joint arthritis in combination with IE.

We present the first case where facet joint arthritis was the presenting symptom for culture-negative A. aphrophilus native valve IE in a patient with no prior cardiac disease. A 58-year-old Japanese male without known cardiac disease, presented with high fever, chills, and lower back pain. Initial laboratory evaluation showed leukocytosis and transaminitis. Transthoracic echocardiography revealed an aortic valve vegetation with moderate aortic regurgitation. Magnetic resonance imaging (MRI) showed high-intensity areas in the right iliopsoas muscle and L4/L5 facet joint, indicative of fluid accumulation and disseminated lesions. Multiple sets of blood cultures showed no bacterial growth. Broad-range polymerase chain reaction (br-PCR) for 16S ribosomal RNA on both blood and hepatocytes (due to the patient’s acute liver damage) also failed to identify the causative organism. The patient developed heart failure, and transesophageal echocardiography showed severe aortic regurgitation and an aneurysm at the noncoronary cusp of the aortic valve with perforation. He underwent aortic valve replacement and his symptoms were promptly improved. Although cultures from the excised valve were negative, br-PCR on the valve tissue eventually confirmed the presence of A. aphrophilus.

This is the first reported case of culture-negative native valve IE caused by A. aphrophilus presenting with facet joint arthritis in a patient without known cardiac disease. Our case emphasizes the importance of considering IE in patients with fever and unexplained musculoskeletal pain, even without known cardiac disease. When conventional diagnostic tests are inconclusive, br-PCR on excised valve tissue is indispensable. Further improvements in non-invasive diagnostic methods are needed to facilitate early diagnosis and treatment.