CASE PRESENTATION

An 81-year-old, left-hand-dominant man presents to the dermatology clinic with a 2-week history of pruritic lesions limited to his left forearm. The patient's clinical history is remarkable for frequent home gardening on a daily basis. Physical examination revealed discrete erythematous papules and subcutaneous nodules in a unilateral distribution (Figure 1). He denies a history of fever or chills. Past treatment with oral antibiotics and topical antifungals has been ineffective.

FIGURE 1. Erythematous papules and nodules showing linear spread confined to the left arm.

Multiple-Choice Question

A. Scabies

B. Arthropod assault

C. Sporotrichosis

D. Cat-scratch disease

E. Pyoderma gangrenosum

DISCUSSION

Answer: C. Sporotrichosis

Sporotrichosis is a fungal infection caused by Sporothrix schenckii and named after Benjamin Schenck who initially described the disease in 1898 (Orofino-Costa et al., 2017). S. schenckii is a dimorphic fungus that results in cutaneous lesions and regional lymphatic involvement after inoculation (Qin & Zhang, 2019). Given the prevalence of the disease in gardeners, it has been referred to as gardener's mycosis (Yu & Zhang, 2021). Lesions of affected individuals typically occur in a unilateral distribution on the extremities and face with distinct papules, eroded nodules, and ulcers. The clinical presentation and underlying morphology of the cutaneous lesions on physical examination raise a high index of suspicion for sporotrichosis, which can be confirmed through fungal culture. A skin biopsy is likely to be nonspecific with findings of granulomatous inflammation and epithelial hyperplasia (Rodrigues et al., 2022). Topical antifungal therapy is generally ineffective as therapy for sporotrichosis. The treatment of choice is a 3- to 6-month course of itraconazole 200-300 mg daily depending on the degree of clinical symptoms (Mahajan, 2014). Itraconazole is a triazole antifungal that inhibits the cytochrome P450 enzyme lanosterol 14 alpha-demethylase, which converts lanosterol to ergosterol, thereby resulting in fungal cell wall destruction (Mahajan, 2014). Before initiating treatment with itraconazole, it is important to conduct a thorough medical history as itraconazole carries a black box warning for new or exacerbated congestive heart failure (Teaford et al., 2020). In addition, by inhibiting the cytochrome P450 system, it is important to avoid prescribing this agent to patients taking drugs metabolized by the cytochrome P450 system such as digoxin and warfarin. For patients who are not candidates for itraconazole, alternative treatment options include saturated solution of potassium iodide, terbinafine, fluconazole, and liposomal amphotericin B (Mahajan, 2014). Before the availability of itraconazole, saturated solution of potassium iodide was the standard of care and still remains a first-line treatment for uncomplicated infections in developing nations because of its low cost and widespread availability (Mahajan, 2014).

Scabies can be differentiated from sporotrichosis based on clinical presentation. Scabies does not typically present in a unilateral pattern and is intensely pruritic, resulting in numerous excoriations being present on physical examination. The pathognomonic sign is the presence of linear burrowing representing the tunnel where mites lay their eggs. Antiscabietic treatments such as permethrin or lindane as well as oral ivermectin are the treatments of choice (Sunderkotter et al., 2021).

Arthropod bites will often present with excoriated papules in a clustered pattern. An antecedent history of outdoor exposure or exposure to arthropods is often elicited during conversation with the patient. The lesions are typically self-limited, but topical corticosteroids can be used to control symptoms and speed resolution.

Cat-scratch disease is notable for persistent, tender regional lymphadenopathy that can last up to several months. The disease is caused by a cat scratch or bite resulting in a bacterial infection with the Gram-negative bacillus, Bartonella henselae (Nawrocki et al., 2020). Oral antibiotics such as azithromycin and doxycycline can be effective in the treatment of cat-scratch disease.

The most common clinical presentation of pyoderma gangrenosum is that of a nonhealing ulcer. Although pyoderma gangrenosum can occur anywhere on the body, it frequently presents on the lower extremities. The initial lesion will be a tender papule or pustule with a surrounding violaceous induration that will eventually undergo necrosis, resulting in ulceration (Alavi et al., 2017). Inflammatory bowel disease and arthritis can frequently be associated with pyoderma gangrenosum. The use of high-potency topical corticosteroids, systemic corticosteroids, and immunosuppressive agents such as cyclosporine has been reported effective in treatment (George et al., 2019).

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