Fungal Spine Infections

Candida Spondylodiscitis

Most common fungal pathogen (50% of cases)

Species: C. albicans most common, but C. glabrata, C. tropicalis, C. parapsilosis increasingly recognized

Risk factors:

• Prolonged ICU stay with central lines
• Total parenteral nutrition (TPN)
• Recent broad-spectrum antibiotics
• Abdominal surgery
• IV drug use

Clinical features:

• Indolent onset over weeks to months
• Back pain with low-grade fever
• Often diagnosed late when neurological deficit develops

Treatment:

• Fluconazole 400-800mg daily PO for susceptible species (C. albicans, C. tropicalis)
• Echinocandin (micafungin 100mg IV daily) for resistant species or critically ill patients
• Duration: minimum 6 months, up to 12 months if extensive disease

Candida has good disc involvement with disc space narrowing on imaging.

Aspergillus Spondylodiscitis

Second most common (25% of cases)

Species: A. fumigatus most common, also A. flavus, A. niger

Risk factors:

• Hematological malignancies
• Hematopoietic stem cell transplantation
• Prolonged neutropenia
• Chronic granulomatous disease
• High-dose corticosteroids

Clinical features:

• More aggressive than Candida
• Prominent bony destruction
• Disc relatively spared initially
• Paravertebral mass common
• High mortality (30-50%) if disseminated

Treatment:

• Voriconazole 6mg/kg IV q12h day 1, then 4mg/kg IV q12h (or 200mg PO BID)
• Alternative: Liposomal amphotericin B 5mg/kg IV daily
• Duration: minimum 12 weeks, often 6-12 months
• Surgical debridement often required due to extensive bony destruction

Aspergillus preferentially destroys bone, resulting in vertebral collapse and kyphotic deformity.

Coccidioides, Histoplasma, Blastomyces

Geographic distribution critical - endemic to specific regions of USA

Coccidioides immitis/posadasii (Southwest USA):

• Primary pulmonary infection, disseminates to spine in 10-50% of disseminated cases
• Chronic granulomatous infection
• Multifocal spine involvement common
• Treatment: Fluconazole 400-800mg daily for 12+ months, or liposomal amphotericin B for severe cases
• Surgery for neurological deficit or instability

Histoplasma capsulatum (Mississippi/Ohio valleys):

• Less common than Coccidioides to involve spine
• Occurs in AIDS patients or chronic granulomatous disease
• Treatment: Itraconazole 200mg TID for 3 days, then 200mg BID for 12+ months

Blastomyces dermatitidis (Great Lakes, Mississippi valley):

• Rare spinal involvement
• Presents with chronic back pain and draining sinuses
• Treatment: Itraconazole 200mg TID for 3 days, then 200mg daily for 6-12 months

Endemic fungi cause chronic granulomatous inflammation with caseous necrosis mimicking tuberculosis clinically and radiographically.

Diagnostic Approach

Imaging Characteristics

Antifungal Therapy by Organism

Monitoring and Follow-up

• Clinical response: Monitor pain, fever, neurological status weekly initially
• Inflammatory markers: CRP and ESR monthly - should trend down over 3-6 months
• Drug levels: Voriconazole trough 1-5.5mcg/mL, itraconazole trough greater than 1mcg/mL
• Toxicity monitoring: LFTs monthly (azole hepatotoxicity), creatinine (amphotericin nephrotoxicity), visual changes (voriconazole)
• Imaging: MRI at 3 months and 6 months to assess response - expect slow radiographic improvement

Failure to improve clinically or radiographically at 3 months suggests need for surgical intervention or change in antifungal regimen.

Indications for Surgery

Absolute indications:

• Progressive neurological deficit (motor weakness, cauda equina syndrome)
• Spinal instability (vertebral collapse, kyphotic deformity greater than 30°)
• Epidural abscess with cord compression
• Medical treatment failure (progression despite 4-6 weeks appropriate antifungals)

Relative indications:

• Tissue diagnosis needed (CT biopsy non-diagnostic or technically difficult)
• Extensive bony destruction requiring reconstruction
• Large paravertebral abscess amenable to drainage

Surgical Approaches

Surgical Principles

Debridement: Remove ALL infected tissue including disc, vertebral body, and paraspinal abscess. Send multiple tissue samples for culture (fungal, bacterial, mycobacterial) and pathology.

Reconstruction: Use structural support (expandable cage, allograft, PMMA if not planning fusion) to restore height and alignment. Avoid autograft (risk of infection).

Instrumentation: Place pedicle screws 2 levels above and below infected segment. Supplement with anterior plate if anterior-only approach. Instrumentation can generally be retained (unlike high-grade bacterial infections).

Postoperative: Continue antifungal therapy 6-12 months postoperatively. TLSO brace for 3 months. Early mobilization when neurologically and hemodynamically stable.

Successful fusion rates 70-80% with combination therapy, compared to 40-50% with medical therapy alone in severe cases.

Prognostic Factors

Outcomes

Candida spondylodiscitis: Favorable outcomes with early diagnosis and treatment. Combination therapy (surgical debridement plus prolonged fluconazole) results in 70-80% cure rate. Neurological recovery occurs in 80-90% of patients undergoing early decompression.

Aspergillus spondylodiscitis: Guarded prognosis with 30-50% mortality if disseminated. Localized spinal aspergillosis has better outcomes (70-80% survival) with aggressive surgical debridement and voriconazole therapy.

Endemic mycoses: Chronic course requiring lifelong suppressive therapy in many cases. Coccidioidomycosis has 60-70% response rate to fluconazole but relapses common if therapy discontinued.