An Unusual Case of Scalp Actinomycosis

Dear Editor, A 10-year-old girl presented to the dermatology outpatient department with multiple swellings on her scalp for the past 4–5 years. Her parents gave a history of trauma to the right forehead when she was 3-years-old, for which she was shown to a local practitioner and received antibiotics. There was no history of vomiting, headache, blurring of vision, weight loss, loss of appetite, or night sweats. Examination revealed multiple nontender, erythematous, granulation-like polypoidal nodules measuring 1 × 1 cm to 5 × 5 cm, discretely arranged with yellow-brown adherent crust and moderate purulent discharge on the scalp [Figure 1a]. There was no evidence of cervical lymphadenopathy. We considered the possibilities of scrofuloderma, soft tissue tumor, actinomycetoma, and scalp actinomycosis. Pus and tissue for cartridge-based nucleic acid amplification tests, Gram stain, aerobic and anaerobic culture, and potassium hydroxide stain and fungal culture were negative. The Mantoux test was negative, and chest X-ray and abdominopelvic sonography did not yield any evidence of tuberculosis. The dihydrorhodamine assay, T-cell, B-cell, and natural killer cell tests for immunodeficiency were negative. Contrast-enhanced computed tomography and contrast-enhanced magnetic resonance imaging showed hyperdense lesions in both parietal lobes with dural thickening, subdural collections with irregularities, sclerosis of the skull bone, and large T1 isointense and T2 hypointense areas, respectively. Biopsy revealed a dense inflammatory infiltrate composed of neutrophils and lymphocytes, with bacterial filaments giving an appearance of Splendore-Hoeppli phenomenon, suggestive of actinomycosis [Figure 1b]. A final diagnosis of scalp actinomycosis was considered and the patient was started on injectable ceftriaxone for 3 weeks due to the unavailability of penicillin. The patient was discharged on oral penicillin G, and complete resolution of the lesion was noted after 1 month of follow-up [Figure 1c].Figure 1: (a) Clinical picture reveals discretely arranged multiple yellow-brown adherent crusted polypoidal erythematous nodules on the scalp. (b) Histopathology depicts inflammatory infiltrates composed of neutrophils, and lymphocytes, with bacterial filaments giving an appearance of Splendore Hoeppli phenomenon [H & E, 40X]. (c) Reduction in number and size of plaques on the scalp after 1 month of therapyActinomycosis is an extremely rare skin and soft tissue infection caused by Actinomyces israeli. Actinomyces is a Gram-positive, filamentous, microaerophilic, or anaerobic bacillus. It is a commensal flora of the oropharynx, gastrointestinal, and urogenital tract.[1]Actinomyces are not able to penetrate healthy tissue; disruption of the epithelial or mucosal barrier is mandatory.[1,2] Actinomycosis is classified into various types based on the site of involvement such as cervicofacial, thoracic, abdominopelvic, and primary cutaneous.[2] Scalp actinomycosis is usually secondary to the respiratory tract, abdomen, pelvis, or cervicofacial routes and following trauma. It is mostly from the hematogenous route. Scalp actinomycosis can be a focal lesion or dural/epidural involvement with parenchymal involvement may occur.[3] It presents as fungating masses, or draining sinuses with tissue fibrosis and sulfur granules. Rarely, cases may present as pseudocarcinomatous or sarcomatous masses.[3] There are few case reports on scalp actinomycosis, making our case an unusual presentation.[1,4,5] Gram stain shows Gram-positive, thin branching, fragmented coccobacilli without spores. Zeihl-Neelsen stain shows non-acid-fast branches with an acid-fast club.[4] It can be isolated from enriched media such as chocolate blood agar, brain heart infusion broth, and Brucella blood agar with hemin and vitamin K1 at 37 °C. Semi-selective media like phenyl ethyl alcohol or mupirocin-metronidazole blood agar increases the isolation rate by inhibiting the overgrowth of other organisms. A. israelii forms a “molar tooth” colony on agar and forms clumps in broth. Biochemical tests such as urease, catalase, and fermentation of sugars usually lead to the misidentification of species.[1,4] Histopathology reveals hyperkeratosis and acanthosis of epidermis. The underlying dermis shows clumps of basophilic filamentous bacteria in a rosette-like configuration, surrounded by neutrophilic infiltrate with granulomatous inflammatory cells composed of lymphocytes, eosinophils, and giant cells, with eosinophilic clubs at the periphery described as Splendore- Hoeppli phenomenon.[1,3,5]Table 1 depicts differentiating actinomycosis from scrofuloderma, actinomycetoma, and nocardiosis.Table 1: Differentiating features of actinomycosis, actinomycetoma, nocardiosis, and scrofulodermaActinomyces species are most sensitive to antibiotics. The drug of choice for actinomycosis is high-dose penicillin therapy for a long period due to fibrotic reaction, which limits drug penetration. Injectable penicillin G (benzylpenicillin) is given at a dose of 18–24 million units/day in, divided doses every 4–6 hours for 4–8 weeks, followed by oral penicillin G till complete resolution, which usually takes 6–12 months. If penicillin is not available, injectable ceftriaxone is a better alternative with good efficacy.[5] In patients having penicillin allergy, tetracycline is an alternative. Other alternatives include erythromycin, clindamycin, clarithromycin, or azithromycin. Antibiotics such as metronidazole and aminoglycosides have no in vitro activity against Actinomyces, but data are limited and controversial.[1,4,5] We hereby present an unusual case of scalp actinomycosis presenting as a soft tissue tumor and also highlight the therapeutic response to ceftriaxone. Declaration of patient consent The authors certify that they have obtained all appropriate parent consent forms. In the form a parent has given his consent for her images and other clinical information to be reported in the journal. The parent understands that her name and initials will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. Use of artificial intelligence (AI) The preparation of this manuscript was carried out entirely by the authors without the use of artificial intelligence technologies.