A 76-year-old Thai woman presented with a 5-month history of bilateral, well-defined, non-healing ulcers on both forearms without systemic symptoms. Her medical history included well-controlled type 2 diabetes mellitus, hypertension, and dyslipidemia. She had never received immunosuppressive medications. The patient reported frequent groundwater exposure but denied recent trauma or animal contact. Physical examination revealed multiple discrete ulcers with well-defined, undermined edges on both forearms (Figure 1a,b). No additional skin lesions, hepatosplenomegaly, lymphadenopathy, or systemic findings were noted. Laboratory investigations, including complete blood count, fasting blood glucose (99 mg/dL), glycated hemoglobin (6.2%), chest radiography, and human immunodeficiency virus (HIV) screening, were unremarkable. The bilateral distribution and characteristic morphology of the ulcers suggested the possibility of chronic inflammatory conditions such as pyoderma gangrenosum. In addition, the chronic course of the lesions warranted consideration of chronic infectious etiologies, including non-tuberculous mycobacterial infection, tuberculosis, and deep fungal infections. Potassium hydroxide preparation and Gram staining of material from the ulcer demonstrated numerous neutrophils but no fungi or bacteria. Fungal cultures were negative. A skin biopsy demonstrated ulcerated and acanthotic epidermis with dermal infiltration of histiocytes, lymphocytes, and neutrophils. Morula-like structures were identified. Grocott methenamine silver (GMS) and periodic acid–Schiff (PAS) staining demonstrated round, variably sized organisms with thick-walled sporangia containing endospores (Figure 2). Culture yielded skin microbiota, with no fungal or mycobacterial growth. Tissue polymerase chain reaction for tuberculous and non-tuberculous mycobacteria was negative. A diagnosis of cutaneous protothecosis was confirmed based on characteristic histopathologic findings. The patient was treated with oral itraconazole (200 mg/day). At 8 weeks, significant improvement was observed, with one lesion healing into a scar. All lesions have been markedly improving without new lesion development over an 8-month follow-up period (Figure 1c,d). Prototheca, an achlorophyllous alga commonly found in water, soil, cow's milk, and animal waste, rarely causes human infection and typically affects immunocompromised hosts. The most frequently implicated species are P. wickerhamii (72.2%) and P. zopfii (16%–22.2%) 1. Cutaneous lesions are the most common presentation, followed by olecranon bursitis and disseminated infection. A review of 54 disseminated cases (1970–2023) found that about 70% occurred in immunocompromised individuals 1. Although diabetes mellitus is a known risk factor, only two disseminated cases involved diabetic patients, one of whom also had systemic lupus erythematosus and received corticosteroids 2. In this case, the bilateral lesions without systemic involvement support a localized form rather than disseminated form. Moreover, her well-controlled diabetes possibly explained not overt immunocompromise and the localized form. Inoculation commonly occurs through skin trauma, though only one-third of cases report injury 3. The patient denied trauma but reported groundwater exposure. Cutaneous protothecosis progresses slowly and presents variably as erythematous papules, plaques, nodules, vesicles, verrucous lesions, ulcers, or herpetiform eruptions. A review of cases from China, Hong Kong, and Taiwan reported papules, plaques, or nodules in 87.8% (15/18) of patients; only 16.7% (3/18) had bilateral involvement. The extensor surfaces, especially the limbs, are most commonly affected 3. The ulcerative, bilateral distribution in this case is relatively uncommon. Due to its non-specific clinical features, protothecosis is frequently misdiagnosed. One study reported misdiagnosis in 50% of cases 1. Diagnosis relies on histopathology (with sporangia resembling morulae, confirmed by special stains), with culture or molecular methods used for confirmation. Most publications reported diagnosis from all histopathology, culture and molecular identification while some reported from morulae characteristics on histopathology alone as our case 4. There is no standardized treatment; however, antifungal therapy, surgical excision, or combination approaches have shown favorable outcomes. Treatment duration ranges from 2 weeks to 1 year. Amphotericin B has demonstrated the highest efficacy, followed by itraconazole and fluconazole; ketoconazole showed the least. Terbinafine has also been used successfully in some cases 5. This report received no external funding. Written informed consent was obtained from the patient for online publication of the clinical details and images. No identifiable personal information has been included in this report. The authors declare no conflicts of interest. Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.
Panjapakkul et al. (Thu,) studied this question.