Keywords
18 F-fluorodeoxyglucose positron emission tomography - computed tomography in spinal
decompression assessment -
18 F-fluorodeoxyglucose positron emission tomography - computed tomography in spinal
tuberculosis - monitoring pott's spine
Introduction
Tuberculosis (TB) of the spine is the most important extra pulmonary TB (ETB), which
can cause significant morbidity and permanent neurological damage. It accounts for
~50% of the cases of ETB and affects about 1%–2% of TB worldwide.[1 ] The most common involvement is seen in the dorsal spine.[2 ]
The lytic destructive variant of spinal TB can destroy the intervertebral discs, vertebral
body, collapse, kyphotic deformity, and spinal cord compression.[3 ]
Magnetic resonance imaging (MRI) has been the cornerstone and preferred standard investigation
for the assessment of the spine in spinal TB.[4 ] 18F-fluorodeoxyglucose (18 F-FDG) positron emission tomography/computed tomography (PET/CT) is a new diagnostic
investigation in infection and inflammation imaging. It maps the radioactive glucose
uptake by the infection/inflammatory process and gives a quantitative assessment using
“Standardized uptake value” (SUVmax ). SUVmax helps to assess the aggressiveness of the disease and can be used to monitor the
therapy response in the follow-up scans.
Depending on the aggressiveness of the disease process, surgical or medical management
of the Pott's spine can be decided. Early surgical decompression can substantially
decrease the morbidity of the patient.
Anti-tubercular treatment (ATT) for Pott's spine has to be taken for 18 months, but
no standard protocol has been set to decide when to stop the treatment.[5 ] Hence, we try to explain the role of follow-up using 18 F-FDG PET/CT scans for assessing the therapy response.
Case Report
The first patient is an 18-year-old female, presented with fever, upper back pain,
lower limb numbness, and restricted movement for 1 month. On examination, she had
low-grade fever and tenderness over the midline at the upper back region. She had
lower limb paraparesis with power 1/5, restricted straight leg raising test, positive
ankle, and knee jerk reflex. Laboratory investigation reveal erythrocyte sedimentation
rate (ESR): 43 mm/h, white blood cell (WBC): 11900 cells/mm3, C-reactive protein (CRP):
34 mg/L. MRI, [Figure 1 ] dorsal spine revealed anterior wedging of T3/T4 vertebral bodies with posterior
cortical bulging (gibbus) causing kyphotic deformity. In addition, altered magnetic
resonance (MR) signal in T2, T3, T4 vertebral bodies along with paravertebral collection
extending from C7 to T5. 18 F-FDG PET/CT [Figure 1 ] done on the next day revealed similar findings as MRI (SUVmax -18.4 in T3/4) and besides, revealed extensive cervical (SUVmax -12.7) and mediastinal lymphadenopathy (SUVmax -13.7). Considering this surgery was planned for the dorsal spine. Intraoperatively,
granulation tissue and destructive bones were removed and the abscess was aspirated.
The dorsal cord was decompressed and a metallic cage with lateral internal fixation
was performed. Histopathology confirmed to be TB and the patient was started on ATT.
Follow-up 18 F-FDG PET/CT [Figure 2 ] scans were done on the 3rd month and 18th month after surgery, which showed complete
resolution of all lesions. The patient regained her full neurological capability in
both the lower limbs.
Figure 2 Baseline scan-{[A(axial),C(sagittal)-T2 weighted Magnetic Resonance Imaging], [B(axial)
& D(sagittal) fused Positron emission tomography/computed tomography]}: Anterior wedging
of T3/T4 vertebral bodies with posterior cortical bulging (gibbus) and kyphotic deformity.
Altered signal intensity & FDG avidity in T2, T3, T4 vertebra. Pre and Paravertebral
soft component extending from C7 to T5 vertebral body level
Figure 2 Positron emission tomography-computed tomography ([a-c; axial, sagittal, maximal
intensity projection], [I-baseline, II-3rd month, III-18th month]) - fluorodeoxyglucose avidity (Standardized uptake value max-18.4) with Anterior
wedging of T3/T4 vertebral bodies associated with posterior cortical bulging (gibbus),
kyphotic deformity and extensive cervical (Standardized uptake value max-12.7)/mediastinal
lymphadenopathy (Standardized uptake value max-13.7). Underwent Lateral Internal fixation
with metallic cage. No fluorodeoxyglucose avid focus at 3rd month and 18th month scan
The second case is a 22-year-old female, complaints of fever, cough, upper back pain,
and lower limb weakness for 21 days. On examination, she had low-grade fever and tenderness
in the upper dorsal region. She had lower limb paraparesis with power 2/5, restricted
straight leg raising test, and positive ankle and knee jerk reflex. Laboratory investigation
reveals ESR: 28 mm/h, WBC: 9800 cells/mm3, CRP: 22 mg/L. MRI [Figure 3 ] of the dorsal spine revealed wedging of T6/T7 vertebral bodies, T6/7 intervertebral
disc changes with epidural soft-tissue causing thecae compression and spinal cord
narrowing. In addition, altered MR signals in T5, T8 vertebral bodies, and prevertebral
collections were seen extending from T5 to T8. 18 F-FDG PET/CT [Figure 2 ] done on the next day revealed similar findings as MRI (SUVmax -16.9 at T6/7), besides revealed extensive right pleural involvement (SUVmax -4.5), right loculated effusion (SUVmax -4.2). Considering this surgery was planned for the dorsal spine. Intraoperatively,
granulation tissue, destructive bone were removed and prevertebral abscess aspirated.
The dorsal cord was decompressed and a pedicle screw with posterolateral internal
fixation was done. Histopathology revealed TB and ATT started. Follow-up 18 F-FDG PET/CT [Figure 4 ] scan done on the 3rd month showed partial resolution of the spinal lesion (SUVmax -4.7) and persistence of located effusion at right cardiophrenic angle (SUVmax -9.7). PET/CT at 18th month showed partial resolution of the T6-7 vertebral lesion
(SUVmax -3.4), a substantial increase in the size and avidity of the right cardiophrenic loculated
pleural effusion (SUVmax -10.3) and appearance of the right oblique fissure effusion (SUVmax -11.2). Hence, there was disease progression. Ultrasonography-guided aspiration of
the cardiophrenic abscess revealed isoniazid isonicotinic acid hydrazide (INH) resistant
TB. She was put on a higher dose of INH and re-evaluated after 3 months. She responded
well with better neurological recovery (power was 4/5).
Figure 3 Baseline scan (a-T1-weighted axial, b-T2-weighted axial, c-Axial positron emission
tomography-computed tomography, d-T1-weighted sagittal, e-T2-weighted sagittal, f-sagittal
positron emission tomography.computed tomography); fluorodeoxyglucose avid (Standardized
uptake value max-16.9), anterior wedging of T6/T7 vertebral bodies with mild posterior
displacement, T6-7 intervertebral disc changes with epidural soft-tissue causing altered
signal intensity on the spinal cord with canal narrowing. Altered marrow signal and
fluorodeoxyglucose avidity (Standardized uptake value max-10.6) was noted in T5/T8.
Prevertebral collection extending from T5 to T8 vertebral body level. * and + symbol
is representation of the disease affected vertebra
Figure 4 Positron emission tomography.computed tomography ([a-c; axial, sagittal, maximal
intensity projection]. [I-baseline, II-3rd month, III-18th month]) - fluorodeoxyglucose avidity (Standardized uptake value max-16.9) in anterior
wedging of T6/T7 vertebral bodies with mild posterior displacement, T6-7 intervertebral
disc changes with epidural soft tissue component, right pleural and right loculated
effusion. Underwent posterolateral internal fixation with the pedicle screw. At 3rd month, positron emission tomography/computed tomography revealed the persistence
of the right loculated effusion at cardiophrenic angle (IIc, orange arrow). At 18th month positron emission tomography/computed tomography, a substantial increase in
the size and avidity of the right loculated effusion at cardiophrenic angle (IIIc,
Orange arrow) and appearance of new oblique fissure effusion (IIIc, Blue arrow)
Discussion
TB spondylitis is seen in countries with a high prevalence of pulmonary TB.[1 ] The most commonly affected spinal site is the dorsal spine.[2 ] TB of any origin presents with weight loss, fever, night sweats, whereas severe
back pain and neurological deficit direct toward spinal TB.[6 ] The disease progressively causes vertebral collapse, destruction, abscess formation,
which trickles to adjacent pre/para/epidural spaces, subsequently causing spinal cord
compression, kyphotic deformity, and neurological deficits.[7 ],[8 ] Our first patient responded beautifully to early surgical decompression and showed
an early complete metabolic response in PET/CT. Whereas our 2nd patient, even though
she had a responding spinal disease, developed loculated pleura effusion, which progressed
in the 3rd PET/CT. On further analysis, it turned out to be INH-resistant TB. Hence,
18 F-FDG PET/CT helped in assessing the whole body of the patient in a single go, thereby
focusing our mind on the actual disease process. Few of the authors have used 18 F-FDG PET/CT as a monitoring marker for assessing the metabolic changes in the course
of therapy.[5 ] Timeline for the assessment of therapy response has been suggested for 6, 12, 18
months for skeletal TB evaluation.[9 ],[10 ]
PET/MRI is a powerful tool in the block, with both functional and anatomical capabilities.
Excellent spatial resolution combined with metabolic evolution and reduced overall
patient radiation dose is a few of the important advantages in comparison to PET/CT.[11 ] Cost is the only limiting factor.
Conclusion
18 F-FDG PET/CT is a one shop stop modality for assessing the whole body disease burden
at the start of the treatment, monitoring the disease response to therapy and help
in guiding the physicians to reach a therapeutic endpoint.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot bechrological order guaranteed.
