Management of Erythema Induratum in an Elderly Patient
Initiate standard anti-tuberculosis therapy immediately with isoniazid, rifampicin, and pyrazinamide for 6 months, as erythema induratum is a tuberculid (hypersensitivity reaction to Mycobacterium tuberculosis) that requires treatment of the underlying tuberculous infection to prevent recurrence and achieve complete resolution. 1, 2, 3
Confirm the Diagnosis and Assess for Active TB
Screen for active tuberculosis with chest X-ray, tuberculin skin test (TST) or interferon-gamma release assay (IGRA), and sputum cultures if pulmonary symptoms are present, as erythema induratum represents a hypersensitivity reaction to M. tuberculosis antigens and may indicate occult tuberculous infection 2, 3, 4
Consider extrapulmonary TB evaluation including abdominal imaging (ultrasound or CT) to assess for hepatic hilum or other extrapulmonary involvement, particularly if initial pulmonary workup is negative, as recent evidence demonstrates hepatic tuberculosis can manifest as erythema induratum even in immunocompetent elderly patients 2
Obtain complete blood count, liver function tests, renal function, and baseline visual acuity before initiating anti-TB therapy to establish baseline values for monitoring drug toxicity 1, 3
Standard Anti-Tuberculosis Treatment Regimen
Prescribe the standard 6-month regimen: isoniazid 5 mg/kg (max 300 mg) daily, rifampicin 10 mg/kg (max 600 mg) daily, and pyrazinamide 25 mg/kg daily for the initial 2 months, followed by isoniazid and rifampicin for an additional 4 months 1, 3, 5
Add pyridoxine (vitamin B6) 25-50 mg daily to prevent isoniazid-induced peripheral neuropathy, which is particularly important in elderly patients who are at higher risk for this complication 1
Monitor monthly for hepatotoxicity (transaminases), gastrointestinal side effects, thrombocytopenia, and visual changes, as elderly patients are more susceptible to anti-TB drug toxicity 1, 3
Alternative Approach if Oral Therapy Not Tolerated
Consider topical isoniazid 3.75% applied twice daily to the affected lower leg lesions if the patient develops severe gastrointestinal upset, significant thrombocytopenia, or hepatotoxicity that precludes oral therapy, as this novel approach has demonstrated complete remission within 2 months without systemic side effects 1
This topical regimen should be continued for 6 months to match the duration of standard systemic therapy and prevent relapse 1
Topical therapy is particularly valuable in elderly patients with multiple comorbidities or polypharmacy who cannot tolerate systemic anti-TB drugs 1
Expected Clinical Course and Monitoring
Expect improvement within 1 month of initiating therapy, with most lesions remitting by 2 months and complete resolution by 6 months 1, 3
The chronic tender erythematous nodules and ulcerations on the lower legs should gradually heal with resolution of pain, though scarring may persist 1, 3
Failure to improve after 2 months of appropriate therapy warrants reassessment for drug resistance, alternative diagnosis, or inadequate treatment adherence 3, 5
Critical Pitfalls to Avoid
Do not treat with NSAIDs, antibiotics, or corticosteroids alone, as these provide only temporary symptomatic relief without addressing the underlying tuberculous etiology and will result in recurrent episodes, as demonstrated by the 4-year delay in diagnosis in one case series 3, 5
Do not assume the diagnosis is erythema nodosum based solely on lower extremity nodules, as erythema induratum has distinct histopathology showing lobular panniculitis with vasculitis and granulomatous inflammation, whereas erythema nodosum shows septal panniculitis without vasculitis 4, 5
Do not discontinue therapy prematurely even if skin lesions resolve, as the full 6-month course is necessary to eradicate the tuberculous infection and prevent relapse 1, 3
Avoid sedating antihistamines if pruritus is present, as elderly patients are at increased risk for falls, confusion, and cognitive impairment from these medications 6, 7
Adjunctive Symptomatic Management
Provide leg elevation and compression stockings to reduce venous stasis and edema in the lower extremities, which may exacerbate the nodular lesions 5
Apply emollients with high lipid content to surrounding dry skin if present, as elderly patients commonly have concurrent xerosis that can worsen discomfort 6
Consider NSAIDs for pain control during the initial treatment phase while awaiting response to anti-TB therapy, though these do not treat the underlying condition 5