Tuberculosis and comorbidities: treatment challenges in patients with comorbid diabetes mellitus and depression

Tuberculosis is one of the leading causes of death worldwide, primarily affecting low- and middle income countries and individuals with limited-resources within fractured health care systems. Unfortunately, the COVID-19 pandemic has only served to aggravate the already existing diagnostic gap, decreasing the number of people who get diagnosed and thereby complete successful treatment. In addition to this, comorbidities act as an external component that when added to the TB management equation, renders it even more complex. Among the various comorbidities that interact with TB disease, diabetes mellitus and depression are two of the most prevalent among non-communicable diseases within the TB population and merits a thoughtful consideration when the healthcare system provides care for them. TB patients with diabetes mellitus (TB-DM) or depression both have an increased risk of mortality, relapse and recurrence. Both of these diseases when in presence of TB present a 'vicious-circle-like' mechanism, meaning that the effect of each disease can negatively add up, in a synergistic manner, complicating the patient's health state. Among TB-DM patients, high glucose blood levels can decrease the effectiveness of anti-tuberculosis drugs; however, higher doses of anti-tuberculous drugs could potentially decrease the effects of DM drugs. Among the TB-depression patients, not only do we have the adherence to treatment problems, but depression itself can biologically shift the immunological profile responsible for TB containment, and the other way around, TB itself can alter the hormonal balance of several neurotransmitters responsible for depression. In this paper, we review these and other important aspects such as the pharmacological interactions found in the treatment of TB-DM and TB-depression patients and the implication on TB care and pharmacological considerations.