Treatment of Erythema Induratum
For a young to middle-aged woman with erythema induratum potentially associated with tuberculosis, initiate standard anti-tuberculosis therapy with isoniazid, rifampin, and pyrazinamide after first excluding active TB disease through chest radiography and clinical evaluation. 1, 2, 3
Initial Diagnostic Workup
Before initiating treatment, active tuberculosis must be ruled out through the following steps:
- Obtain chest radiography immediately to identify pulmonary TB, cavitary lesions, or fibrotic changes consistent with prior TB 4, 5
- Perform tuberculin skin testing (TST) or interferon-gamma release assay (IGRA) to document TB infection; a positive result is defined as ≥5 mm induration for immunocompromised patients or ≥10 mm for other high-risk individuals 4, 6
- Collect sputum specimens for mycobacteriologic testing only if chest radiograph is abnormal or respiratory symptoms are present 4, 5
- Consider biopsy of skin lesions showing necrotizing granulomatous inflammation with vasculitis, though M. tuberculosis may not be detected in cutaneous samples even when present elsewhere 7
Standard Treatment Regimen
The recommended approach is standard anti-tuberculosis therapy, not treatment for latent infection alone, as erythema induratum represents an immunologic response to active or occult TB:
- Initial phase (2 months): Rifampin, isoniazid, and pyrazinamide in combination 8, 1, 3
- Continuation phase (4-6 months): Rifampin and isoniazid 8, 2
- Total duration: Minimum 6 months of therapy, with clinical response typically observed within 1-2 months 1, 3
Dosing Considerations
- Rifampin is indicated for all forms of tuberculosis when organisms are susceptible, and should be part of a multi-drug regimen to prevent resistance 8
- Isoniazid is recommended for all forms of tuberculosis with susceptible organisms, always used with multiple concomitant medications 9
- Add pyridoxine (vitamin B6) supplementation with isoniazid-containing regimens to prevent peripheral neuropathy 10, 5
Alternative Treatment Options
If standard oral therapy is not tolerated:
- Topical anti-tuberculosis therapy (3.75% isoniazid applied twice daily) may be considered for patients who develop severe gastrointestinal upset or hematologic toxicity from oral medications, with clinical improvement expected within 1-2 months 1
- Symptomatic management with nonsteroidal anti-inflammatory drugs, potassium iodide, or colchicine can be used as adjunctive therapy for non-tuberculous cases 2
Monitoring During Treatment
- Baseline liver function tests are mandatory before starting therapy, particularly for patients with risk factors including HIV infection, pregnancy, or history of liver disease 10, 6
- Monitor liver enzymes every 2-4 weeks during treatment and educate patients about hepatotoxicity symptoms (nausea, vomiting, jaundice) 6, 5
- Monthly clinical evaluations to assess treatment response and medication adherence 10
Critical Caveats
- Erythema induratum in adolescents or young adults should prompt aggressive investigation for underlying active TB, as cutaneous manifestations may be the presenting sign of cavitary pulmonary disease 3
- Consider extrapulmonary TB involvement (hepatic hilum, lymph nodes) even when pulmonary imaging appears normal, as M. tuberculosis may be detected only in non-cutaneous sites 7
- Do not treat as isolated latent TB infection with single-agent therapy, as erythema induratum represents an active immunologic process requiring full multi-drug anti-tuberculosis treatment 2, 3
- Non-tuberculous nodular vasculitis may occur in patients with inflammatory bowel disease or other conditions; if TB is definitively excluded through negative testing and no response to anti-TB therapy, consider alternative diagnoses 11