Histopathology of Scrofuloderma
Characteristic Histopathological Features
The histopathology of scrofuloderma demonstrates epithelioid granulomatous inflammation with caseating necrosis, though the specific findings vary depending on the stage of disease and the patient's immune status. 1, 2
Core Microscopic Findings
Epithelioid granulomas are the hallmark feature, consisting of aggregates of epithelioid histiocytes with or without Langhans giant cells 1, 2
Caseating necrosis is typically present in the center of granulomas, representing tissue destruction from the underlying tuberculous focus (lymph node, bone, or joint) 1, 2
Acid-fast bacilli (AFB) staining is frequently negative on histopathologic examination, even when culture is positive for Mycobacterium tuberculosis 1, 2
Suppurative inflammation may be prominent, with neutrophilic infiltrates and abscess formation, particularly in active draining lesions 2
Variations Based on Immune Status
Immunocompetent patients typically show well-formed granulomas with organized epithelioid cells and minimal organisms on special stains 2
Immunocompromised patients may demonstrate atypical histopathology with poorly formed granulomas, increased numbers of acid-fast bacilli, and more extensive necrosis 2
Critical Diagnostic Pitfalls
Negative AFB stains do not exclude the diagnosis - culture and molecular testing (PCR) are essential even when histopathology shows classic granulomatous inflammation but AFB stains are negative 1, 2
Histopathology alone cannot distinguish between M. tuberculosis and atypical mycobacteria (MAIS group) - bacteriological culture and molecular identification are mandatory 3
The epidermis may be uninvolved in early lesions, with pathology confined to the dermis and subcutaneous tissue overlying the tuberculous focus 2
Essential Diagnostic Workup
Tissue culture from skin biopsy is more sensitive than smears from discharge, and should always be performed when scrofuloderma is suspected 1, 3
Cartridge-based nucleic acid amplification test (CBNAAT) should be obtained to confirm M. tuberculosis and detect rifampicin resistance, as drug-resistant disease is increasingly common 4
PCR confirmation provides rapid species identification when culture results are pending 1, 3
Treatment Implications
Standard anti-tubercular therapy for drug-susceptible disease consists of an intensive phase with four drugs (rifampicin, isoniazid, ethambutol, pyrazinamide) followed by a continuation phase 3
Drug susceptibility testing is mandatory before finalizing treatment, as rifampicin resistance requires multi-drug regimens for 24 months 4
Complete regression of lesions typically occurs with appropriate anti-tubercular therapy, confirming the diagnosis retrospectively 1