Verrucous cutaneous lesions on the arm of unusual origin

A 55-year-old woman from Afghanistan presented with multiple reddish lesions on the left forearm that appeared 8 weeks prior. Of note, after infiltration of a carpal tunnel syndrome 2 years ago, she had developed recurrent phlegmons on the left forearm. This had led to an ulcer which was covered by a split skin graft 1.5 years ago.

The clinical examination showed several livid-erythematous, partially hyperkeratotic plaques, measuring up to 3 cm, on the dorsal left forearm (Figure 1). These non-painful plaques presented with expression of pus on pressure. In addition, solitary erythematous papules on the skin graft as well as on normal skin of the left forearm could be observed. The rest of the skin was unremarkable. There was no palpable lymphadenopathy and no systemic symptoms like fever were reported. A skin biopsy was made (Figure 2a).

Tuberculosis verrucosa cutis

A skin biopsy showed a pseudoepitheliomatous hyperplasia with a dense dermal superficial lympho-histiocytic inflammatory infiltrate including multinucleated giant cells, suggesting an infectious cause (Figure 2a). Immunohistochemistry confirmed the abundance of CD68+ macrophages (Figure 2b). Acid-fast staining (Ziehl-Neelsen) and a broad-spectrum polymerase chain reaction from the tissue specimen were negative for fungal and bacterial species including Mycobacterium tuberculosis. However, the culture obtained from this skin tissue confirmed the presence of M. tuberculosis complex 6 weeks later. The computed tomography (CT) of the thorax showed pleural consolidations, compatible with former tuberculosis (TB), supported by a positive interferon gamma release assay (IGRA). Further organ involvement could be ruled out via CT and MRI. Sputum specimens were negative for M. tuberculosis. The patient's husband and daughter also had a positive IGRA, but there was no active TB in the patient's social environment.

The patient received a standard tuberculostatic therapy which consisted of an oral combination of rifampicin, ethambutol, pyrazinamide, and isoniazid for 2 months, followed by a treatment with rifampicin and isoniazid for 4 months. The lesions showed remission with just remaining post-inflammatory hyperpigmentation (Figure 3). The IGRA-positive relatives were treated with rifampicin for 4 months.

Extrapulmonary tuberculosis (TB) accounts for approximately 10%–15% of all TB cases and usually manifests as lymphadenitis, pleuritis, or osteoarticular TB.^{1, 2} Cutaneous forms of TB are very rare, comprising approximately 1%–2% of all TB cases.³ They can present as different clinical phenotypes, for example, ulcers, nodular lesions, abscesses, and verrucous lesions, depending on different factors such as the route of infection, immunity of the infected individual and previous sensitisation to M. tuberculosis.⁴

Tuberculosis verrucosa cutis (TVC) is a rare (4.3%) form of cutaneous TB that occurs in previously sensitised individuals with good immunity.⁵ The route of infection is exogenous via inoculation through wounds with infectious sputum or contaminated objects.⁶ Based on this, the bacterial load within the skin varies in these different forms of cutaneous TB. In multibacillary forms (i.e., tuberculous chancre, scrofuloderma, orificial TB, acute miliary TB, and metastatic abscess/tuberculous gumma), bacilli are easily detected in tissue, while in the less common paucibacillary forms (i.e., TVC, lupus vulgaris) it is difficult to prove the organisms.⁴ In countries of the global north infections are rare and usually associated with specific professions such as butchers, farmers and pathologists resulting in lesions on the hands.⁷ For the latter this had led to the historic term of ‘prosector's wart’ or ‘postmortem wart’.⁷

In our case, the chronic wound on the left forearm is considered as the entry point for the pathogen.

This case illustrates that cutaneous TB, though a rare form of extrapulmonary TB and even rarer in countries of the global north, needs to be considered in the differential diagnosis of an unusual ulceration. While the overall sensitivity of PCR in cutaneous TB is 73%, it decreases in cases of pauci-bacillary forms, like TVC, to 56%.⁸ Therefore diagnostic procedures to detect paucibacillary mycobacterial infections are challenging and must include microscopy from tissue samples, PCR and—in particular—culture since the load of mycobacteria may vary and be below the PCR detection threshold. All three should be performed in every patient and should be repeated in case of initially negative results but persisting suspicion of cutaneous TB.

Substantial contributions to conception and design, or acquisition of data, or analysis and interpretation of data: Luisa Unterluggauer, Liliane Borik-Heil, Philipp Tschandl and Nicole Harrison. Drafting manuscript: Luisa Unterluggauer and Liliane Borik-Heil. Critically revising the manuscript for important intellectual content: Liliane Borik-Heil, Philipp Tschandl and Nicole Harrison. Final approval of the version to be published: all authors.

The authors declare no conflict of interest.

All patients in this manuscript have given written informed consent for participation in the study and the use of their deidentified, anonymized, aggregated data and their case details (including photographs) for publication. Ethical approval: not applicable.