A Rare Case of Primary Cutaneous Actinomycosis Masquerading as Chronic Granulomatous Infection

Dear Editor, We wish to highlight a rare case of primary cutaneous actinomycosis that clinically mimicked a chronic granulomatous infection, posing a significant diagnostic challenge. A 47-year-old male presented with multiple painful, pus-discharging skin lesions over the back for 10 years. The lesions began as a swelling which gradually spread across the upper back, developing multiple sinuses and crusting [Figure 1]. The patient had been previously treated with multiple antibiotics and antifungals but without a complete resolution. Notably, there was no history of trauma, a typical precursor for primary cutaneous actinomycosis.Figure 1: Clinical image showing multiple indurated plaques and nodules with honey coloured crusts predominantly on the upper backCutaneous examination revealed indurated erythematous plaques and nodules with multiple serosanguinous and purulent discharging sinuses, along with atrophic scarring and local rise of temperature. Laboratory findings included leukocytosis (WBC 16,300/cu mm) and elevated C-reactive protein (24 mg/dl). Imaging studies suggested soft tissue inflammation without systemic involvement. Gram staining of pus revealed Gram-positive bacilli, while acid-fast bacilli and fungal elements were absent. Histopathology demonstrated hyperkeratosis, irregular acanthosis, and dense dermal inflammation with microabscesses composed of neutrophils, eosinophils, lymphocytes, and macrophages [Figures 2 and 3]. These findings, in correlation with clinical features, pointed to a diagnosis of actinomycosis.Figure 2: Histopathological image showing dermis with marked dense inflammatory infiltrate. [H and E 40x]Figure 3: Mixed dermal infiltrate composing of eosinophils, neutrophils, lymphocytes and macrophages. [H and E 100x]Actinomycosis is a chronic suppurative infection caused by Actinomyces species, often presenting with discharging sinuses and sulfur granules. While cervicofacial, thoracic, and abdominal forms are common, primary cutaneous involvement is extremely rare, especially without preceding trauma. Diagnosis hinges on clinical suspicion, histopathology, and microbiological correlation, though cultures may be non-contributory due to fastidious growth requirements.[1-3] In our case, classical clinical features and histopathology facilitated diagnosis despite the absence of trauma or positive culture findings. The patient was allergic to Penicillin; hence, he was treated with a tailored oral antibiotic regimen: Doxycycline (100 mg BID), Metronidazole (400 mg BID) for 6 months, Amoxicillin-Clavulanic acid for 1 month, and topical Mupirocin.[4,5] Dramatic clinical improvement was noted within 3 months, with complete healing at 6 months [Figure 4].Figure 4: Image taken after 6 months of treatment showing complete resolution of the lesions with only atrophic scars leaving behindThis case emphasises the importance of including actinomycosis in the differential diagnosis of chronic granulomatous dermatoses, especially in non-resolving cases. Its ability to masquerade as tuberculosis or deep fungal infections can lead to misdiagnosis and prolonged morbidity. In such cases, clinicopathological correlation remains crucial. Additionally, a high index of suspicion is required even in the absence of trauma. We report this case to reinforce awareness about this rare cutaneous presentation and to advocate for early biopsy, histopathological evaluation, and immediate treatment intervention in atypical dermatoses. Consent Informed written consent was obtained from the patient. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.