Keywords
Aspergillus terreus
- fungal infection - spondylodiscitis - surgical site infection - osteomyelitis
Introduction
Spondylodiscitis refers to an infection of the spine and accounts for 2 to 7% of pyogenic
osteomyelitis cases.[1] Fungal spondylodiscitis is rare[2] with an incidence of 0.6 to 1.6% in various studies among all spondylodiscitis cases.[3]
[4] Postoperative fungal spondylodiscitis is even rarer but is increasing worldwide
due to prolonged spine surgeries, particularly in elderly and immunocompromised patients.[5]
Candida and Aspergillus are the commonest fungi infecting the spine.[6]
Aspergillus terreus is an extremely rare cause of discitis.[7] We present a case of A. terreus spondylodiscitis following lumbar spine surgery in a healthy female patient. To the
best of our knowledge, this is the only case reported in the literature of an A. terreus spondylodiscitis in an otherwise healthy patient.
Case Report
A 39-year-old female with mild diabetes presented to us with back pain and bilateral
leg pain with numbness of 3-year duration. She was thoroughly investigated and after
a trial of conservative treatment failed to relieve her symptoms, she was advised
surgery. X-rays ([Fig. 1]) and magnetic resonance imaging (MRI) lumber spine (LS) ([Fig. 2]) showed left postero-lateral disc extrusion with inferior migration and canal stenosis
L4–5. The patient underwent posterior decompression, stabilization, and interbody
fusion L4–5. The postoperative period was uneventful and patient was mobilized and
discharged.
Fig. 1 Plain radiographs of lumbosacral spine—AP and lateral views showing decreased lordosis,
calcified posterior annulus L4–5. AP, anteroposterior.
Fig. 2 MRI LS spine T2 weighted images showing extruded and inferior migrated disc fragment,
facet effusion and stenosis. LS, lumber spine; MRI, magnetic resonance imaging.
Six weeks later she presented with fever, back pain, and left leg pain with raised
erythrocyte sedimentation rate and C-reactive protein. There was serous discharge
from the wound. Contrast MRI ([Fig. 3]) showed hyperintensity at L4–5 disc with an abscess dorsal to the dura.
Fig. 3 Six weeks post-surgery contrast MRI LS spine T2-weighted images showing epidural
collection with peripheral enhancement dorsal to the dura with disc hyperintensity
at L4–5. LS, lumber spine; MRI, magnetic resonance imaging.
In view of surgical site infection, thorough debridement was done. Samples sent for
microbiological and fungal cultures grew A. terreus, sensitive for voriconazole. Microbiologist and infection control specialist's opinions
taken. Antifungal drug sensitivity with minimum inhibitory concentration (MIC) values
is available in very few centers in the world and is not available in our region,
3 years ago. According to Berkow EL and Lockhart SR et al[8], identifying the pathogen accurately can sometimes allow for the empirical selection
of an antifungal drug without requiring susceptibility testing. For instance, in the
United States, Aspergillus is typically treated with voriconazole empirically, as
resistance to this antifungal has not been widely observed. Furthermore, for fungal
pathogens lacking established interpretive criteria, such as breakpoints or epidemiological
cutoff values, obtaining an MIC value might not provide a definitive clinical interpretation.
Moreover, voriconazole is a first-line treatment according to Infectious Diseases
Society of America (IDSA) guidelines for Aspergillus species.[9] Hence, the patient was started on intravenous voriconazole for 2 weeks followed
by oral therapy.
Six weeks after starting antifungal therapy, the patient was significantly relieved
of her leg pain but moderate back pain persisted. A contrast MRI ([Fig. 4]) revealed a 10 mm intradural granuloma at L3 level and hyperintensity of L4–5 disc.
Blood parameters gradually returned to normal with no constitutional symptoms. The
patient was closely monitored and oral antifungal therapy was continued for a total
duration of 6 months as advised by infectious disease specialists. At the end of 6
months of antifungal therapy, the patient had no fever or any back pain, with normal
blood parameters and hence was decided to stop the therapy.
Fig. 4 Follow-up contrast MRI LS spine sagittal images showing intradural granuloma behind
L3 body with reduced bony and disc edema.
At three and half years post-surgery, there was no relapse and ([Fig. 5]) the patient was asymptomatic and was back to her activities of daily living.
Fig. 5 Three and half year follow-up X-ray showing no evidence of any bony destruction or
implant loosening.
Discussion
Aspergillosis is primarily a respiratory pathogen but can rarely involve the musculoskeletal
system, with 50% of cases affecting the spine.[2]
[10]
Sources of infection include contagious lung spread, hematogenous spread, and direct
inoculation (trauma/surgery), with hospital-acquired infections linked to immune-compromised
hosts and construction/renovation sites.[11] Immune dysfunction predisposes individuals with risk factors.[2]
[7]
[11] Around one-third of patients affected have no predisposing factors.[12]
Clinical presentation is nonspecific[7] with an overall mortality rate of 25%, hence the need for high index of suspicion
and accurate diagnosis.[2]
[7]
[13] Laboratory tests are often not useful.[13] Recently, biomarkers such as galactomannan and serum β D-glucan have been used to
confirm the diagnosis.[14] Definitive identification of A. terreus is through culture in sabouraud dextrose agar (SDA) medium, showing cinnamon-brown
colonies, smooth-walled conidiophores, and biseriate conidial heads.[7] Radiological findings depend on patient's immunity and disease severity. Differentials
are other fungal infections, tuberculosis, and pyogenic discitis.[15]
Till now, only eight human cases of A. terreus spondylodiscitis have been reported but none of them occurred after lumbar spine
surgery in a healthy patient. One resulted from direct inoculation (stab injury),[10] two from hematogenous spread,[16]
[17] two from contiguous lung spread,[18]
[19] one from a vascular surgery complication,[20] one with multifocal bone involvement,[21] and one from traumatic inoculation.[7]
In our patient, we hypothesize that the source of infection could be from an adjacent
operation theater where renovation work was going on. Although this area was isolated,
we suspect that the fungus could have infected via the air-conditioning ducts which
may not have been sufficiently packed. This is our suspicion in retrospect and we
cannot be sure of this hypothesis.
Management involves surgical debridement and long-term antifungal therapy for 6 to
12 months, with voriconazole as first-line treatment according to IDSA guidelines.
For refractory patients, itraconazole is recommended.[5]
[7]
[9] Precautions to reduce fungal infections include patient optimization, strict aseptic
protocols, and avoiding surgeries during renovations in high-risk patients.
Conclusion
Aspergillus terreus is an extremely rare postoperative spinal pathogen. This is the first reported case
in the literature of A. terreus spondylodiscitis following lumbar spine surgery in a healthy patient. Our patient
underscores the need for high index of suspicion, fungal cultures in all suspected
postoperative spinal infections, early and thorough debridement, and appropriate antifungal
therapy.
