Should dry spinal tuberculosis be managed differently than wet spinal tuberculosis?

Background context: On radiopathological examination of spinal tuberculosis (TB), 2 predominant forms are known: dry and wet types. Wet TB, as the name suggests, has abscess formation as its predominant presenting feature and is the exudative form; dry TB includes caseation and sequestration with minimal exudate. Dry TB often exhibits poorer recovery patterns than the wet counterparts, which can be possibly ascribed to vasculitis, ischemia, or tubercular myelitis, rather than isolated mechanical compression. These pathologic processes may lead to neurological deficit which is less responsive to treatment.

Purpose: To quantify the recovery and prognosis, and test for the significance of difference between neurological recovery pattern and prognosis of the 2 forms of spinal TB.

Design: A retrospective analytical observational study design in the form of a cohort study was performed.

Patient sample: Single-center patient data over 6 years was analyzed. Of 217 patients with spinal TB, 18 had dry TB (Group 1). Two patients were excluded because they presented very late after the onset of neurological deficit, which could have played a role in the nonrecovering nature of motor weakness. The remaining patients had wet TB, of which 22 patients were selected for propensity score matching to form a comparison group.

Outcome measures: Radiological measures included vertebral body height loss, deformity, canal encroachment, cord diameter, altered cord signal intensity and loss of CSF space. Functional measures were ambulatory status of the patient at final follow-up and neurologic status measured by ASIA (American Spinal Injury Association) and LEMS (Lower Extremity Motor Score) scoring.

Methods: The criteria for dry TB were imaging suggestive of granulation tissue (heterogenous hypo- or hyper-intensity on T2WI sequence), with at least 1 of the 2 factors (1) absence of anterior or posterior epidural abscess formation within the spinal canal (2) a canal encroachment of <30%. The groups were compared with respect to their differences in demographic distribution, symptom complex, mycobacterial drug sensitivity and presence of history of tuberculosis elsewhere in the body. Analysis was done by various tests of significance depending on the type of variable. Bar charts and Pie charts were used for visual representation of the analyzed data. Level of significance was set at 0.05.

Results: Dry TB showed partial or no return to ambulation (75% vs. 31.5% in wet, p=.01) at 12-months and took more time to reach final ambulatory level (9.16 months vs. 2.9 months in wet), despite having a lower average Cobb angle (16.5 degrees versus 20.95 in wet (p=.132), lower mean canal-encroachment (24.9% vs. 50.09% in wet, p<.01) and preserved posterior-CSF flow as compared to wet TB (p=.02). At final follow-up, 4/16 (25%) of dry and 0% of wet TB were ASIA A, and 9/16 (56.25%) dry and 18/22 (72.7%) of wet TB were ASIA E (p=.04).

Conclusion: Dry TB of the spine has poorer functional outcome in terms of time to ambulation and final ambulatory status despite having minimal destruction and abscess formation causing mechanical cord compression.