Initial presentation of acute myelogenous leukemia in the infiltrate underlying an actinic keratosis.

We report an 85-year-old female patient who presented with an erythematous keratotic lesion on her temple suspicious of squamous cell carcinoma. Histological evaluation revealed actinic keratosis, but the underlying atypical infiltrate contained atypical myeloid forms consistent with acute myelogenous leukemia (AML). Upon further questioning, it was determined that the patient had a history of myelodysplastic syndrome. Her skin biopsy provided the first evidence of progression to AML. This case serves as an important reminder of the role the dermatopathologist plays in identifying serious systemic disease.

INTRODUCTION

Myeloid leukemia cutis (LC) may be the presenting sign in patients with myeloid disorders, like acute myelogenous leukemia (AML). It occurs in approximately 13% of patients with AML[1] and classically presents later in the disease, when neoplastic leukocytes of myeloid lineage infiltrate the epidermis, dermis, or subcutis.[2] In some cases, however, the appearance of LC is the first evidence of leukemia and the atypical myeloid forms can be identified in the infiltrate underlying an unrelated skin lesion. The clinical appearance of the skin lesions is fairly non-specific and as in this case, the clinical appearance may reflect only the superficial cutaneous neoplasm, rather than the underlying leukemia. A high index of suspicion is required as correct interpretation of the biopsy leads to the correct diagnosis and allows early intervention.[34] In our patient, the biopsy was performed for confirming a keratotic lesion; but the underlying leukemia proved to be the more important diagnosis.

CLINICAL

An 85-year-old-female patient presented with skin lesions on her right temple and left nasal sidewall, suspicious for squamous cell carcinoma (SCC). Shave biopsies of the areas were performed.

DERMATOPATHOLOGY

The lesion on right temple demonstrated an actinic keratosis (AK) with an underlying dermal infiltrate of immature myeloid cells [Figures 1 and 2]. Immunohistochemical staining for myeloperoxidase [Figure 3], CD68 and CD34 supported a diagnosis of myelogenous leukemia.

Figure 1

Actinic keratosis with underlying immature myeloid cells. Hematoxylin-eosin stained sections, ×100

Figure 2

Underlying dermal infiltrate of immature myeloid cells. Hematoxylin-eosin stained sections, ×400

Figure 3

Myeloperoxidase stain in cells of myeloid lineage, ×200

DISCUSSION

AML may present as an isolated papule or nodule, but the manifestations may be as diverse as an erythematous, pruritic, morbilliform eruption or patches and plaques mimicking mycosis fungoides.[5] Leukemic cells may also be recruited to areas of inflammation.[6] A diagnosis of LC in the presence of AML is a poor prognostic indicator and strongly correlates with additional sites of extramedullary involvement.[7] This can alter the appropriate treatment regimen for a patient, making the diagnosis of particular importance.

The diagnosis rests on the recognition of immature myeloid cells within the cutaneous infiltrate. The cells commonly demonstrate hyperchromasia, amphophilic cytoplasm and a tendency toward single filing between collagen bundles. Nuclear molding may be noted. Any myeloid cell line may be represented, including immature neutrophils, eosinophils or basophils. Epidermal changes are usually minimal, but may be the most prominent finding in cases such as ours when the biopsy is performed because of the overlying unrelated skin lesion. Patients presenting with LC in association with non-melanoma skin cancer have including those with SCC and basal cell carcinomas.[8] In our patient, the overlying epidermal changes were diagnostic of AK and it might have been easy to overlook the more important diagnosis of leukemia. Dermatopathologists need to remain sensitive to the possibility of a critical diagnosis within the infiltrate underlying a common cutaneous lesion.