Not Your Average Back Knot - Page #4
 

Working Diagnosis:
Spinal Tuberculosis (Pott’s Disease). Affecting facet joints and spinous processes of T12-L1

Treatment:
Initial treatment for osteomyelitis with vancomycin + cefepime without improvement in patient condition. T-spot returned positive on hospital day 4, along with the acid-fast stain of the abscess fluid. The TB culture was positive shortly after.

Treatment was initiated with rifampin, isoniazid, pyrazinamide, ethambutol on hospital day 4. He was followed closely by health department for a full 9 months of treatment.

Outcome:
At 1-month follow-up, the patient had no subjective concerns and near-complete resolution of his low back pain. He had full return to physical activity at 6 weeks after initiation of antibiotics. He is scheduled for a follow-up spine Xray at 12 months from diagnosis to evaluate for gibbus deformity.

Patient had no history of BCG vaccine or known sick contact in Cameroon. On further research, his initial tuberculin skin test had an induration of 13mm which was read as positive. He did have a chest x-ray on immigration which did not reveal any active disease, but was not aware of any further need for follow up for latent TB infection treatment.

Author's Comments:
Tuberculous spondylitis is caused by the acid-fast bacterium mycobacterium tuberculosis. It is spread to the vertebrae via arterial hematogenous spread from an active site such as the lungs. The diagnosis of spinal TB is defined as the presence of: 1) relevant clinical signs, which include classical tuberculosis symptoms and back pain which is more often inflammatory than mechanical; 2) imaging signs suggestive of spondylodiscitis or spondylitis; 3) positive bacteriological findings on any sample. TB spondylitis is a non-pyogenic vertebral osteomyelitis (along with syphilis and fungal infection). Histologically, the classic TB lesion consists of granulomatous inflammation with central necrosis, which frequently presents clinically as a “cold abscess.” The ultrasound in our patient was consistent with a more pyogenic infection (although inter-rater reliability can be an issue with ultrasound), which is why biopsy is essential. In these cases, CT-guided fine needle aspiration has been shown to be equivalent to surgical biopsy for diagnostic purposes. Other diagnostic findings include those on MRI or CT.

Most common location is lower thoracic/upper lumbar vertebrae, as was present in our patient. A majority of patients will be left with chronic back pain without loss of function (60%). Few will have resulting paraplegia (4%), and up to 15% will have some neurologic deficit. Absence of neurological involvement indicates a better overall prognosis, and disk space involvement frequently leads to long-term deformity concerns. A common long term complication is Gibbus deformity, or structural kyphosis Case Photo #10, resulting from vertebral collapse placing the spinal cord at risk of compression and possible paraplegia. This may occur decades from the initial infection. Many of the studies looking at prognosis after Pott’s disease have short follow-up and typically include cases with surgical intervention (which was not the case for our patient). Thus, there are no guidelines for long term orthopedic follow up. In general, patients should recover to their previous clinical status within 6 months of treatment initiation for spinal TB, with inflammatory labs resolving sooner around 3 months. MRI abnormalities may often persist after 12 months, even in optimally treated patients. These abnormalities do not require further intervention in patients who have an otherwise favorable outcome.

A common question asked during our treatment was, “Why no Vitamin B6?” Although this pearl still shows up on board exams, the CDC actually only recommends B6 supplementation (25mg/day) with INH dosing in select populations. From the CDC MMWR:
“Peripheral neuropathy occurs in less than 0.2% of people taking INH at conventional doses. It is more likely in the presence of other conditions associated with neuropathy such as diabetes, HIV, renal failure, and alcoholism. Pyridoxine (vitamin B6) supplementation is recommended only in such conditions or to prevent neuropathy in pregnant or breastfeeding women.”

Editor's Comments:
Central to this case is the workup for LTBI in a patient born in a TB endemic country. 10mm induration or greater in medical personnel or recent immigrants is a positive TST result. Our patient had 13mm induration with a negative chest Xray, suggesting no active disease. However, he was lost to follow up for consideration of treatment of latent TB infection. If there are concerns about TST interpretation, the CDC recommends blood testing for confirmation (T-spot or Quantiferon).

Clues to diagnosis of a tuberculous abscess is its “cold” appearance compared to a pyogenic abscess – slow growing, cool to touch, minimally tender. This lesion also had a complex appearance on ultrasound. Simple abscesses usually appear much more straight forward with areas of fluid and perhaps some debris as opposed to the comparatively more homogenous appearance of this mass.

Centers for Disease Control and Prevention. Target tuberculin testing and treatment of latent tuberculosis infection. MMWR 2000;49(No. RR-6):1-42.

References:
Ansari S, Amanullah MF, Ahmad K, Rauniyar RK. Pott's Spine: Diagnostic Imaging Modalities and Technology Advancements. N Am J Med Sci. Jul 2013;5(7):404-11
Centers for Disease Control and Prevention. Treatment of Tuberculosis, American Thoracic Society, CDC, and Infectious Diseases Society of America. MMWR 2003;52(No. RR-11)
Cheung WY, Luk KD. Clinical and radiological outcomes after conservative treatment of TB spondylitis: is the 15 years' follow-up in the MRC study long enough?. Eur Spine J. May 8 2012
Leibert E, Haralambou G. Tuberculosis. In: Rom WN and Garay S, eds. Spinal tuberculosis. Lippincott, Williams and Wilkins; 2004:565-77.
Le Page L, Feydy A, Rillardon L, et al. Spinal tuberculosis: a longitudinal study with clinical, laboratory, and imaging outcomes. Semin Arthritis Rheum. Oct 2006;36(2):124-9.
"Pott Disease" www.http://emedicine.medscape.com/article/226141-overview; Accessed November 1, 2013 via the web.

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