What anti-tuberculosis (TB) medication is likely causing tingling numbness at the tips of the hands in a patient taking vitamin supplements and recently diagnosed with TB?

Isoniazid-Induced Peripheral Neuropathy in Tuberculosis Treatment

Isoniazid (INH) is the most likely cause of the tingling numbness at the fingertips in this patient who has been on anti-TB treatment for three months. 1

Mechanism and Clinical Presentation

Peripheral neuropathy is the most common neurotoxic effect of isoniazid. This adverse effect is:

• Dose-related and occurs most frequently in:

  • Malnourished patients
  • Those predisposed to neuritis (e.g., alcoholics, diabetics)
  • "Slow acetylators" of the drug 2

• Typically presents as:

  • Paresthesias (tingling, numbness) of hands and feet
  • Usually begins distally and can progress proximally if untreated
  • Sensory symptoms often precede motor involvement 3

Risk Factors

Several factors increase the risk of developing isoniazid-induced peripheral neuropathy:

• Malnutrition
• Diabetes mellitus
• HIV infection
• Alcoholism
• Chronic renal failure
• Pregnancy and lactation
• Advanced age
• Slow acetylator status 1, 4

The patient in this case was taking vitamin supplements, which suggests potential recognition of nutritional concerns, but these may have been insufficient to prevent neuropathy.

Prevention and Management

1. Preventive measures:

   • Pyridoxine (vitamin B6) supplementation (10 mg daily) is recommended for patients at increased risk of neuropathy 1
   • Higher doses (25-50 mg daily) are recommended for all persons at risk of neuropathy including those with HIV, diabetes, alcoholism, malnutrition, or chronic renal failure 1

2. Management of established neuropathy:

   • Continue isoniazid if possible (especially if part of a critical regimen for drug-resistant TB)
   • Increase pyridoxine dosage to therapeutic levels (100-250 mg daily) 4
   • Consider reducing isoniazid dose in slow acetylators 4
   • Monitor for symptom improvement

Differential Diagnosis

While isoniazid is the most likely culprit, other considerations include:

• Ethambutol: Primarily causes optic neuritis rather than peripheral neuropathy 1
• Pyrazinamide: More commonly causes arthralgia, hepatitis, and rash rather than neuropathy 1
• Rifampicin: Rarely causes peripheral neuropathy; more commonly causes hepatotoxicity, gastrointestinal upset, and "flu-like" syndrome 1

Common Pitfalls to Avoid

1. Failing to provide prophylactic pyridoxine to high-risk patients
2. Mistaking symptoms for other causes of neuropathy (HIV-related, diabetes, etc.)
3. Discontinuing isoniazid prematurely when dose adjustment and pyridoxine supplementation may be sufficient
4. Inadequate pyridoxine dosing - therapeutic doses (100-250 mg) are much higher than preventive doses (10-50 mg)
5. Overlooking acetylator status - slow acetylators may need dose reduction of isoniazid 4

In conclusion, the clinical presentation of tingling numbness at the fingertips after three months of anti-TB treatment is highly characteristic of isoniazid-induced peripheral neuropathy, which is the most common neurotoxic effect of this medication.