Orthopaedic Surgery - Discitis

Basics

Discitis is an infection involving the intervertebral disc space and adjacent vertebral endplates.

The infection may occur through hematogenous spread or after direct inoculation during a spinal procedure.

Although the lower lumbar spine is affected most often, discitis can involve any intervertebral level.

Classification

Discitis may be classified as spontaneous or hematogenous, in which infection reaches the disc through the bloodstream, or iatrogenic, occurring after procedures such as discectomy or discography.

The infecting process may be pyogenic, granulomatous, or, rarely, parasitic.

Pyogenic Infection

Pyogenic discitis is most commonly caused by Staphylococcus aureus.

Other organisms become more important in immunocompromised patients, intravenous drug users, and patients exposed to healthcare-associated infections.

Granulomatous Infection

Granulomatous disc infection may occur with tuberculosis and other chronic infectious processes.

These infections often have a slower course and may cause more extensive adjacent vertebral destruction.

Epidemiology

Hematogenous discitis is uncommon.

The mean age of spontaneous childhood discitis has historically been reported at approximately 7 years, although the condition can occur at any age.

Incidence

The reported incidence of discitis and related spinal infection is approximately 4–24 cases per million people per year.

Risk Factors

Important risk factors include diabetes mellitus, alcohol misuse, organ transplantation, immunosuppression, intravenous drug use, and procedures that enter or approach the disc space.

Examples of iatrogenic risk include discography, discectomy, and spinal procedures.

Etiology

The causative organism varies according to age and host factors.

Staphylococcal species are the most common pathogens in routine pyogenic infection.

In compromised hosts and intravenous drug users, gram-negative aerobic organisms and fungal pathogens such as Candida become more important.

Kingella kingae

In young children, particularly between approximately 6 months and 4 years of age, Kingella kingae is an important cause of osteoarticular infection and may be responsible for discitis.

Pediatric Vascularity

Young children are particularly susceptible because the disc and adjacent endplate region have a richer blood supply than in adults.

Until approximately 8 years of age, vessels may cross the cartilaginous endplate from the adjacent vertebral body, facilitating hematogenous spread into the disc region.

Associated Conditions

Discitis may coexist with or progress into vertebral osteomyelitis.

In advanced disease, the distinction between disc infection and adjacent vertebral infection may become less clear because both structures can be involved.

Diagnosis

General Principles

The diagnosis is established through a combination of clinical findings, laboratory studies, and imaging.

No single test is sufficient in every case.

Signs and Symptoms

The most common symptom is back pain, usually insidious in onset and progressively worsening.

Children may present less specifically, with abdominal pain, reduced appetite, irritability, malaise, or refusal to walk.

Back Stiffness

Spinal stiffness is common.

Patients may avoid flexing the spine because movement increases pain.

Refusal to Walk

Young children may refuse to stand, walk, or sit normally even when they cannot clearly localize their pain.

This can be an important presenting feature.

Pain With Spinal Percussion

Tenderness or pain with percussion over the affected spinal level may be present.

Loss of Lordosis

Lumbar discitis may cause flattening of the normal lumbar lordosis because of protective muscle spasm.

Fever

Fever is often low grade and may be absent.

The lack of fever does not exclude discitis.

Physical Examination

Lumbar Alignment

The examiner should determine whether normal lumbar lordosis is maintained or reduced.

Loss of lordosis may reflect pain and paraspinal muscle spasm.

Forward Flexion

Patients may have pain or refuse to bend forward.

This is often one of the most useful functional signs during examination.

Paraspinal Percussion

Gentle percussion over the spine may reproduce focal pain.

Abdominal Examination

Lumbar discitis can occasionally present with abdominal pain.

The abdomen should therefore be palpated, particularly in children with poorly localized symptoms.

Neurologic Examination

The neurologic examination is usually normal.

Neurologic deficits are more concerning for advanced infection, epidural involvement, abscess, or neural compression.

Laboratory Tests

White Blood Cell Count

The white blood cell count may be mildly elevated but can remain normal.

A normal count therefore does not exclude infection.

ESR and C-Reactive Protein

The erythrocyte sedimentation rate and C-reactive protein are commonly elevated, but the rise may be modest.

Either marker can occasionally be normal, particularly early in the disease course.

Blood Cultures

Blood cultures should be obtained when discitis is suspected.

However, they are positive in fewer than approximately 30% of cases in some series.

Biopsy

Direct biopsy with microbiologic analysis provides the most definitive method of identifying the causative organism.

Biopsy is particularly useful in immunocompromised patients, atypical infections, or cases that fail to respond to empiric treatment.

Imaging

Plain Radiographs

Plain radiographs are often normal early in the disease.

Abnormalities may not become visible until several weeks after symptoms begin.

Radiographic Findings

Later findings include disc-space narrowing, irregularity of the vertebral endplates, and mild adjacent osseous destruction.

MRI

MRI is the preferred imaging modality for suspected discitis because it can demonstrate infection before changes become visible on radiographs.

It provides excellent anatomic detail of the disc, endplates, vertebral marrow, epidural space, and surrounding soft tissues.

Bone Scan

Bone scintigraphy can be used when MRI is unavailable or contraindicated.

However, degenerative changes may cause false-positive findings, and MRI generally provides superior anatomic information.

FDG-PET

FDG-PET may help distinguish spinal infection from degenerative abnormalities in selected cases.

Its use is generally reserved for situations in which conventional imaging is inconclusive.

Pathological Findings

Discitis produces chronic inflammatory change with destruction of the intervertebral disc and adjacent endplates.

As infection progresses, the distinction between discitis and vertebral osteomyelitis may become less pronounced.

Differential Diagnosis

Tuberculous Spondylodiscitis

Tuberculosis should be considered, particularly when there is extensive vertebral body destruction, paraspinal involvement, or a more indolent clinical course.

Tuberculous disease often produces greater bony destruction than routine pyogenic discitis.

Vertebral Osteomyelitis

Vertebral osteomyelitis primarily affects the bone, whereas discitis begins in the disc and adjacent endplates.

In practice, the two processes frequently overlap.

Treatment

General Principles

Treatment usually consists of appropriate antibiotic therapy for approximately 6–8 weeks.

Surgery is reserved for selected patients with neurologic compression, severe pain, major bone destruction, abscess requiring drainage, instability, or failure of medical treatment.

Rest

Relative rest may be helpful during the painful early phase.

Immobilization

A brace may be used when pain is significant or when additional support is needed.

Prolonged unnecessary immobilization should be avoided once symptoms begin to improve.

Antibiotic Therapy

Antibiotics should target the most likely organism initially and then be adjusted if culture results identify a specific pathogen.

The route of therapy depends on illness severity and patient age.

Childhood Spontaneous Discitis

In otherwise healthy children with typical spontaneous discitis, empiric treatment directed against common pathogens is often successful.

Routine biopsy or operative debridement is not always required when the clinical picture is classic and the child responds appropriately.

Intravenous Versus Oral Therapy

Severely ill patients generally require intravenous antibiotics initially.

Mildly affected patients may be treated orally in selected circumstances, with close follow-up.

Compromised Host

In immunocompromised patients or those with atypical risk factors, biopsy and drainage are more strongly indicated because unusual organisms are more likely.

Physical Therapy

Physical therapy is generally not required during the acute painful phase.

In adults with persistent stiffness after infection control has begun, therapy may help restore spinal mobility, strength, and function.

Medication

Routine Antibiotic Coverage

Historically, agents such as oxacillin, dicloxacillin, or cephalosporins have been used for susceptible staphylococcal infection.

Current empiric therapy should reflect local resistance patterns and patient-specific risk factors.

MRSA Coverage

Because methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen in both hospital and community settings, vancomycin or another appropriate anti-MRSA agent may be required, particularly in severe cases.

Broad-Spectrum Coverage

Complicated infections and infections in compromised hosts may require broader coverage against gram-negative and anaerobic organisms, depending on the clinical scenario.

Pain Control

NSAIDs or short-term mild opioid analgesics may be used for severe pain during the acute phase until the infection comes under control.

Surgery

Indications for Biopsy

Biopsy is especially appropriate in the immunocompromised patient, the patient with atypical infection, or the patient who fails to improve with empiric medical therapy.

Biopsy Approach

Biopsy can be performed through an anterolateral or posterolateral route with imaging guidance.

Percutaneous image-guided techniques are commonly used when feasible.

Drainage and Debridement

Patients who fail to improve with medical treatment or who develop abscess, neurologic compression, or substantial tissue destruction may require surgical drainage and debridement.

Anterior Approach

An anterior approach may provide direct access to the involved disc space and vertebral endplates for decompression and debridement in selected cases.

Reconstruction

Adults with extensive destruction of the disc space or vertebral endplates may require spinal reconstruction to restore stability and alignment.

Minimally Invasive Techniques

Endoscopic or minimally invasive discectomy and drainage may be used in selected adults.

These techniques are less commonly required in children.

Follow-Up

Prognosis

The overall prognosis is generally good once the infection is successfully eradicated.

Children usually recover particularly well.

Childhood Outcome

After childhood discitis, the vertebrae adjacent to the infected disc may undergo spontaneous, painless fusion.

This usually does not cause major long-term functional problems.

Adult Outcome

In adults, spontaneous fusion is less reliable.

Residual chronic back pain or stiffness may persist even after the infection has resolved.

Complications

Persistent Infection

Failure to improve clinically within approximately 1–2 weeks should raise concern for an incorrect organism, inadequate antimicrobial coverage, abscess formation, resistant infection, or the need for debridement.

Neurologic Complications

Although uncommon, advanced infection can cause epidural extension, neural compression, or neurologic deficit.

These findings require urgent evaluation.

Structural Destruction

Severe infection can produce substantial endplate and vertebral destruction, resulting in deformity or instability.

Patient Monitoring

Clinical examination is one of the most useful methods for following recovery.

The examiner should monitor pain, tenderness to percussion, spinal flexibility, gait, and general function.

Laboratory and Radiographic Follow-Up

ESR and radiographic changes often lag behind clinical improvement.

Persistent radiographic abnormalities do not necessarily indicate treatment failure if symptoms and inflammatory markers are improving.

MRI or repeat imaging should be reserved for patients whose clinical course is atypical or worsening.