In 50% to 64% of cases, bone involvement may be the first disease manifestation.6,7,16,22 Osseous involvement with blastomycosis most commonly affects the long bones15 but may include the vertebrae,1-29 the ribs,26 and the carpal or tarsal bones.7,16 The most common vertebral involvement occurs in the thoracic or lumbar spine1,2,7-9,11-14,17,19,21-24,26 and typically results in destruction of the body, development of a paraspinal abscess, and potential extension into the spinal canal, causing an epidural abscess and development of chronic draining cutaneous sinuses.2,7,9,11-13,16,17,19,22,23,26,28,29 In the present case, we do not know whether the vertebral body was involved before the patient presented with mid-thoracolumbar back pain. There may have been bony involvement during initial presentation.
Diagnosis is often difficult because of a low index of suspicion, leading to a significant delay in treatment. Primary pulmonary infections are successfully diagnosed 86% of the time from sputum and 92% of the time from bronchoscopy.19 Once the infection involves the spine, plain radiographs, CT, and magnetic resonance imaging (MRI) can be used to identify not only the bony involvement but also any adjacent soft-tissue extension.13 The radiographic findings, typical of tuberculosis or a neoplasm, include disc space narrowing, vertebral body destruction and collapse, late segmental kyphotic deformity, and development of a psoas abscess or a retropleural abscess.7,26 Such abscesses lend themselves well to fine-needle aspiration,7,8,11,13,14,17,19,26 which, when combined with CT and MRI guidance, reliably assists in the diagnosis of blastomycosis.1,13,17 If fine-needle aspiration fails, then open biopsy and surgical débridement specimens may be effective in the diagnosis.2,9,12,21,22,27
The mortality rate for systemic blastomycosis exceeded 90% before the development of antifungal medications, and these medications remain the primary treatment for most initial infections.15 For severe infections in critically ill patients and for patients with CNS involvement, amphotericin B has been effective, with cure rates approaching 97%.17 Itraconazole, which is well tolerated, has replaced ketoconazole as the preferred long-term oral treatment for blastomycosis. Cure rates for itraconazole approach 90% when treatment is instituted over 2 years in a compliant patient.10,19,20 Nonsurgical (antifungal) treatment for blastomycosis of the spine has also proved successful in neurologically intact patients.7,9,11,26,28
A case involving the spine and requiring surgical drainage was first reported in 19085; since then, only a few more cases have been reported.1,2,5,7-9,11-14,16,17,19,21-24,26-29 Thus, the literature includes very little information that can be used to establish indications for surgery for a blastomycotic infection of the spine. However, there is enough evidence to establish that surgery is indicated for patients who have a known blastomycosis infection and are developing neurologic or structural loss of integrity of the spinal column or have an abscess that requires drainage and débridement.
Our patient had been on long-term antifungal treatment but nevertheless developed a destructive spinal lesion with a concurrent epidural and retropleural abscess. Given his risk of pathologic fracture, we performed anterior débridement and stabilization followed by posterior fusion and instrumentation. We are unaware of any other cases in which an anterior titanium cage was combined with rib autograft after anterior débridement and vertebrectomy combined with posterior instrumentation for blastomycosis. This technique proved very useful, as it allowed for immediate stabilization of the spine. Therefore, the treatment goal is similar to that for any destructive infection that fails medical treatment: preservation of neurologic function, stabilization of spinal vertebrae, débridement of abscess cavity, and definitive culture procurement.
Conclusion
Although there is little reported information regarding surgical indications for blastomycotic vertebral osteomyelitis that has failed medical management—in patients with a destructive lesion and compromise of both the spinal canal and the integrity of the vertebral column—anterior débridement and stabilization followed by posterior fusion and instrumentation are useful in preventing vertebral collapse, further canal compromise, and possible cord injury.