Recent research sheds new light on the impact of diabetes on TB, as well as how TB treatment can affect diabetic control.

Gisela Schecter, MD, MPH, a Curry National Tuberculosis Center (CNTC) Warmline consultant and MDR-TB consultant with the California TB Control Branch, shares a summary of recent studies that increase our understanding of the complexities of co-managing TB and diabetes. A few highlights of her review:

• There is increased risk of progression to active TB among patients with diabetes. A Harvard meta-analysis (Jeon and Murray, 2008) looked at 13 observational studies that included over 1.7 million participants and found that the relative risk (of active TB) is 3-fold higher among those with diabetes.
   
• In presentation and diagnosis, there is an increased likelihood of lung lesions confined to the lower lobes. In one study (Alisjahbana, et al, 2007) this difference was 2.4% without diabetes, to 23.5% with diabetes. Diagnosis may be delayed because the radiologist and treating physician may not "think TB" without upper lobe abnormalities present.
   
• Response to treatment: The old dogma used to be that despite the increased risk of LTBI progressing to active TB among diabetics, these patients did just as well on treatment. A Texas study (Restrepo, et al, 2008) found that diabetics on average achieved sputum culture conversion 5 days later than non-diabetics. A study in Taiwan (Wang, et al, 2008) showed significantly higher mortality among diabetics. Of note, about 1/3 of their TB patients had diabetes.
   
• Effect of TB treatment on diabetes: It is widely known that Rifampin affects the levels of anti-retrovirals used to treat HIV through its effect on the CyP450 enzyme system. Both sulfonylureas (such as glipizide) and thiozolidinediones (such as Avandia or Actos) are metabolized by this same system, so blood levels of these drugs may be lower when Rifampin is being used and therefore diabetes control may suffer. Careful monitoring is required.
   
• Diabetics also have a higher incidence of peripheral neuropathy while taking isoniazid for active TB or LTBI. To protect against this complication, give vitamin B6 at a dose of 25 – 50 mg daily routinely to diabetics whenever INH is prescribed.

Later this year, CNTC will be presenting a national webinar on diabetes and TB to share additional clinical perspectives about this important topic.

References
 
Alisjahbana B, Sahiratmadja E, Nelwan EJ, Purwa AM, Ahmad Y, Ottenhoff TH, Nelwan RH, Parwati I, van der Meer JW, van Crevel R. The effect of type 2 diabetes mellitus on the presentation and treatment response of pulmonary tuberculosis. Clin Infect Dis. 2007 Aug 15;45(4):428-35.Epub 2007 Jul 5.
 
Jeon CY, Murray MB. Diabetes mellitus increases the risk of active tuberculosis: a systematic review of 13 observational studies. PLoS Med. 2008 Jul 15;5(7):e152
 
Restrepo BI, Fisher-Hoch SP, Smith B, Jeon S, Rahbar MH, McCormick JB; Nuevo Santander Tuberculosis Trackers. Mycobacterial clearance from sputum is delayed during the first phase of treatment in patients with diabetes. Am J Trop Med Hyg. 2008 Oct;79(4):541-4.
 
Wang CS, Yang CJ, Chen HC, Chuang SH, Chong IW, Hwang JJ, Huang MS. Impact of type 2 diabetes on manifestations and treatment outcome of pulmonary tuberculosis. Epidemiol Infect. 2008 Jun 18:1-8. [Epub ahead of print]