Advanced Imaging in the Diagnosis of Rare Infectious Spondylodiscitis

Introduction:

Spondylodiscitis is a spinal infection that poses a great set of difficulties in diagnosis. The main factor responsible for this is the rarity of the disease, followed by an extremely common symptom of the disease: lower back pain. This rare infection is reported to occur in individuals above 50 years of age. Males are at a higher risk of developing infectious spondylodiscitis compared to females, the male-to-female ratio being 2:1. The incidence of vertebral osteomyelitis has been observed to increase in recent times due to both the increase in susceptibility to acquiring it as well as the invention of improved diagnostic tools to confirm its occurrence. Spondylodiscitis involves infection of a singular intervertebral disc and the adjacent vertebrae. The spinal column is composed of 32 vertebrae in total, each comprising its vertebral disc. The infection of an isolated disc is quite rare in occurrence, hence the name rare infectious spondylodiscitis. This article discusses the pathogenesis and various diagnostic approaches opted to confirm the disease.

What Causes Spondylodiscitis?

Spondylodiscitis is reported to be associated with various microorganisms, namely bacteria, Mycobacteria, fungi, and Parasites. However, it is observed to be a monomicrobial disease, meaning only one class of microorganisms is responsible for its incidence.

• Staphylococcus aureus is reported to be the most common pathogen and accounts for about half of all non-tuberculous infections.

• Secondary to S. aureus, Enterobacteriaceae is responsible for about 7 to 33 percent of spondylodiscitis cases. This particular class of bacteria commonly includes Escherichia coli, Proteus, Klebsiella, and Enterobacter species.

• Pseudomonas aeruginosa is also said to be involved in several cases of spondylodiscitis. However, it is a rare causative agent.

• Staphylococcus epidermis is also a commonly found species that may contribute to spondylodiscitis.

• Streptococci and Enterococci account for about 5 to 20 percent of spondylodiscitis cases and are observed to be strongly associated with endocarditis infections.

• Other potential microorganisms that may play a role in the occurrence of spondylodiscitis include Streptococcus pneumoniae, Propionibacterium acnes, Bacteroides fragilis, and Brucella melitensis.

• Tuberculosis is proven to be the most common cause of spinal infections, accounting for about 9 to 46 percent of spondylodiscitis cases. About 1 to 3 percent of tuberculosis patients show skeletal manifestations that mainly include the spinal column.

• Spondylodiscitis caused by fungal organisms is reported less frequently, as it rarely causes spinal infection.

An already existing infection involving the genitourinary tract, skin and soft tissue, gastrointestinal tract, respiratory pathways, or the oral cavity is almost always noted in all spondylodiscitis cases. The use of intravascular devices is also observed to be found in about 5 percent of spondylodiscitis patients. Several predisposing factors are identified, such as diabetes mellitus, advancing age, prolonged drug use, immunosuppression, malignancy, renal failure, rheumatic diseases, and liver diseases. A previously encountered spinal injury may also be included in possible risk factors for spondylodiscitis.

What Are the Symptoms of Spondylodiscitis?

The symptoms of infectious spondylodiscitis are highly variable. One may find symptoms that may even misguide the clinician into a wrong diagnosis or, even worse, administering the wrong treatment plan. A tender spine is the most common clinical feature recorded upon physical examination of the patient.

1. Neck and back pain are common in almost all spondylodiscitis patients. However, about 15 percent of total cases are reported to be pain-free in the data collected previously. The pain may or may not be constant and is said to aggravate more during the night. Oftentimes, pain may be referred to the chest or abdomen region, resulting in a complete misdiagnosis and, in some unfortunate cases, an unnecessary surgical procedure.

2. Neurological symptoms include leg weakness, paralysis, sensory deficit, radiculopathy, and sphincter loss.

3. Being an insidious infection, fever is also reported in approximately half of spondylodiscitis patients. However, it is a rare symptom.

4. Tuberculosis-associated spondylodiscitis shows signs of spinal deformities such as kyphosis, and gibbus formation. Dysphagia (trouble swallowing) may be present in patients suffering spondylodiscitis affecting the cervical spine.

5. The spine's range of motion is often restricted and rarely accompanied by sciatic pain.

6. The pediatric population may present with symptoms like irritability, limp-walking, inability to sit or walk for long, unwillingness to crawl, loss of lower back mobility, and reduced lumbar lordosis.

How Is Spondylodiscitis Diagnosed?

The diagnosis of infectious spondylodiscitis often poses a sincere challenge to clinicians. The clinical picture, as discussed above, aids in the diagnosis of the disease. However, it is not sufficient to form a confirmed diagnosis. Laboratory tests and radiological imaging tests complement the diagnosis procedure well, and the result of all 3 summed up can provide a better understanding of the insidious disease.

The laboratory findings may include:

1. An increased level of serum alkaline phosphatase (ALP).

2. A raised C-reactive protein is observed in the majority of the cases.

3. The leucocyte count is reported to be raised in about one-third of spondylodiscitis patients. However, it is considered to be the least beneficial marker.

4. The ESR (erythrocyte sedimentation rate) is said to be raised in about 90 percent of patients.

The microbiological tests are of high value when attempting to obtain a confirmed diagnosis of the spinal infection. A select wide range of microorganisms are said to cause the rare infectious disease. Identifying the causative agent can bring the doctor several steps closer to a final diagnosis.

The radiological examination is said to play a pivotal role in the diagnostic procedure.

• Plain radiograph marks for about 73 percent accuracy and can reveal early changes such as subchondral radiolucency, a deformed endplate, and loss of normal disc height. However, these changes take time to appear. As a consequence, false positives may be incurred, leading to misdiagnosis.

• Computed tomography has proved to be the best radiographic modality that reveals bony abnormalities involving early endplate destruction, or calcification encountered due to tuberculosis. Changes in the disc show up as hypodense regions. Currently, CT is widely utilized for spinal biopsy radiological guidance.

• Magnetic resonance imaging (MRI) is the preferred choice of radiological modality for spondylodiscitis. The MRI is said to be 94 percent accurate with the anatomical features, especially related to the epidural space and the spinal cord. Infective lesions can be differentiated from degenerative changes with much ease in an MRI scan compared to other radiographic modalities.

• Other advanced imaging modalities include radionuclide imaging, which uses a variety of tracers to aid in obtaining a clearer visual. Examples include Technetium-99m–methylene diphosphonate bone scintigraphy, Gallium-67 scintigraphy, and Fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET).

Conclusion:

Spondylodiscitis, although rare, is a miserable infection of the spine and may afflict severe clinical manifestations involving the neurological, and musculoskeletal systems of the body. One may potentially become disabled in cases of chronic infections receiving no appropriate treatment. The mortality rate is quite significant and is highly related to uncontrolled sepsis. Several patients have shown recurrence of infection despite achieving complete recovery from previous infection. Spondylodiscitis in children is reported to show excellent prognosis compared to adults.