Can isoniazid (Isonicotinic Hydrazide) cause neuropathy involving the medial arms and torso?

Isoniazid-Induced Neuropathy Can Affect the Medial Arms and Torso

Yes, isoniazid can cause neuropathy affecting the medial arms and torso, though it more commonly affects the extremities first. 1 Isoniazid-induced peripheral neuropathy typically begins with distal symptoms but can progress to involve more proximal areas including the medial arms and torso if not addressed promptly.

Mechanism and Presentation

Isoniazid-induced neuropathy occurs through:

• Competitive inhibition of pyridoxine (vitamin B6) metabolism 2
• Interference with nerve axon function leading to axonal degeneration 3
• Development of ultrastructural changes in neurons, including:
  • Swelling of axonal mitochondria
  • Disruption of axoplasmic ground substance
  • Accumulation of dense bodies within neurons 3

The typical progression of symptoms includes:

1. Initial presentation with paresthesias (numbness/tingling) in feet and hands 1
2. Progression to more proximal areas including medial arms and torso if untreated
3. Development of motor symptoms with weakness and loss of deep tendon reflexes 3
4. Potential for permanent nerve damage if intervention is delayed 3

Risk Factors

Certain populations are at higher risk for developing isoniazid-induced neuropathy:

• Malnourished individuals 3
• Alcoholics 3, 1
• Diabetics 1
• HIV-infected patients 4
• Slow acetylators (genetic variation) 4, 5
• Elderly patients (risk increases with age) 3
• Pregnant and lactating women 4
• Patients with renal failure 4
• Patients on other neurotoxic medications 4

Prevention and Management

For prevention:

• Pyridoxine (vitamin B6) supplementation should be prescribed for all patients on isoniazid therapy, particularly those with risk factors 3, 2
• Recommended dosage: 25-50 mg/day of pyridoxine for prevention 6
• Higher doses (up to 100 mg/day) may be needed if neuropathy develops 6

For management of established neuropathy:

1. Consider reducing isoniazid dosage to 3 mg/kg/day or less in slow acetylators 4
2. Increase pyridoxine supplementation to 100-250 mg/day 6, 4
3. Monitor for improvement of symptoms
4. In severe cases, discontinuation of isoniazid may be necessary 7

Important Caveats

• Pyridoxine itself can cause peripheral neuropathy at very high doses (>500 mg/day) 6, 8
• Symptoms may persist for months even after appropriate intervention 5
• Nerve conduction studies may be normal in early stages 7
• Morphological changes in nerves can occur before clinical symptoms appear 3
• Recovery may be incomplete if treatment is delayed, with some patients experiencing persistent sensory impairment even after two years 5

Monitoring Recommendations

• Regular clinical assessment for early symptoms of neuropathy (monthly) 3
• Particular vigilance in high-risk patients
• Patient education about early symptoms to report (numbness, tingling, burning sensations)
• Prompt intervention when symptoms appear

Early recognition and management of isoniazid-induced neuropathy is essential to prevent progression to more proximal areas like the medial arms and torso, and to reduce the risk of permanent neurological damage.