June 2017

A 39-year-old male with a lesion on his back

Charles Schultz, MD, Michael Lynch, MD

A 39-year-old male presented for evaluation of a lesion on his upper back that had been present for about one year. Several attempts to treat the lesion with incision and drainage as well as antibiotics had been made previously without success. The lesion continued to grow and concern arose for underlying malignancy.  The patient denied having systemic symptoms or any medical history pertinent to his current illness.

Physical exam showed a 4-centimeter verrucous plaque without surrounding erythema or pigmentation on his upper back.  A shave biopsy was performed.

Hematoxylin and eosin (H&E) stained sections of the shave biopsy of skin demonstrate marked pseudoepitheliomatous hyperplasia with parakeratosis and spongiosis (Figure 1). Large neutrophilic microabscesses were seen within the epidermis and dermis (Figure 2). There is a dense suppurative and granulomatous dermal infiltrate with scattered foreign body multinucleated giant cells (Figure 3). Large yeast forms, some with broad-based budding, are identified on H&E (Figure 4) and highlighted by Periodic acid schiff (PAS) and Grocott methenamine silver (GMS) (Figure 5).

Figure 1. (H&E 10X) Squamous hyperplasia with parakeratosis, spongiosis, and dense dermal inflammatory infiltrate.

Figure 2. (H&E 10X)  Neutrophilic microabscesses in acanthotic epidermis.

Figure 3. (H&E 20X) Mixed dermal infiltrate with neutrophils, histiocytes and multinucleated giant cells.

Figure 4. (H&E 40X) Few large, variably sized yeasts with thick capsules. Both extracellular and phagocytized forms are present.

Figure 5. (GMS 40x) Yeast showing broad-based budding.


What is the diagnosis ?


Please select an answer above.


North American blastomycosis is a dimorphic fungal infection which can cause pulmonary disease and cutaneous deep fungal infections. The infectious agent, Blastomyces dermatitidis takes the form of a mold below 30o C and exists as 7-15 mm yeast with a thick, refractile cell wall, which stains with mucicarmine, above 35o C.1,3-4

Endemic to the Mississippi, St. Lawrence, and Ohio River valleys and regions surrounding the Great Lakes, blastomycosis has an annual incidence of 40/100,000 in the United States with risk factors including residence near waterways or exposure to decaying wood.4 Unlike opportunistic fungal infections, blastomycosis is no more likely to infect immunocompromised patients, though infection in an immunocompromised patient tends to be more severe with disseminated infection.3-4

Infection with blastomycosis ranges from a subclinical respiratory infection or isolated skin lesion to severe disease disseminated disease with cutaneous, genitourinary tract, bone or central nervous system (CNS) involvement.3-5 Isolated respiratory disease is seen in the majority of patients with associated systemic symptoms including weight loss, fever, night sweats and cough.3

In those with extra-pulmonary disease, 40-80% of patients develop cutaneous lesions. The cutaneous lesions include verrucous plaques, dermal nodules or abscesses.1,6 Initial misdiagnosis is common and many of these lesions are incised and drained, leading to ulcerated lesions with an exudative base.6-7 Isolated skin infection also occasionally occurs via traumatic inoculation. 1,8

An established verrucous lesion displays marked pseudoepitheliomatous hyperplasia with a mixed dermal inflammatory infiltrate containing neutrophils, histiocytes, and giant cells. Neutrophilic microabscesses are seen within the dermis and within the hyperplastic epidermis. Loosely formed granulomas and suppurative granulomas can also be seen.1 The thick-walled yeast is found in the center of the abscesses or within giant cells. Although usually identifiable on H&E sections, GMS and PAS stains can help highlight the yeast.1,9-10

The histologic differential diagnosis is broad and includes many deep fungal infections including sporotrichosis, paracoccidioidomycosis, coccidioidomycosis, chromoblastomycosis, and phaeohyphomycosis, other infectious etiologies such as atypical mycobacteria, actinomycosis, and blastomycosis-like pyoderma, and halogenoderma.1

This differential can usually be parsed out by utilization of special stains including a GMS or PAS for fungi, gram stain for bacteria, and an AFB stain for mycobacteria and a close review of available clinical information.  If histopathologic examination fails to identify organisms, tissue culture becomes imperative, and is still considered the most sensitive method for detection.3,10

Itraconazole is the first line treatment for mild to moderately severe blastomycosis; however, in more severe cases, such as in immunocompromised patients or those with CNS involvement, amphotericin B may be needed.3



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