Light-Brown Macule on the Upper Arm
THE DIAGNOSIS: Pigmented Bowen Disease
Histopathology revealed atypical keratinocytes throughout the entire thickness of a pigmented epidermis extending from the basal layer (Figure). Diffuse epidermal hyperpigmentation and melanophages in the papillary dermis were present. There was no dermal invasion or atypical melanocytic proliferation. On dermoscopy, this lesion had small brown globules, smudging, and an asymmetric nonspecific homogeneous pattern. Based on these features as well as the clinical findings, a diagnosis of pigmented Bowen disease (PBD), a rare subtype of squamous cell carcinoma in situ, was made. Complete removal of the lesion was achieved via the biopsy, and the patient was counselled regarding the malignant but noninvasive nature of the lesion. Appropriate follow-up was recommended to monitor for recurrence.
Our case presentation of PBD on the right upper arm in a female patient with a light skin tone is not classic, as PBD lesions usually manifest as well-demarcated scaly plaques on sun-protected sites in men with darker skin tones who are in the sixth to seventh decades of life.1
Dermoscopy of PBD in patients with lighter skin tones can present diagnostic challenges because characteristic clustered glomerular vessels may be faint or absent, particularly in small lesions such as this one. In such cases, PBD may instead demonstrate structureless brown pigmentation and irregular globules, patterns that overlap with pigmented actinic keratosis (PAK) and melanoma.3
Our case underscores the importance of maintaining a broad differential when evaluating small pigmented macules and reinforces biopsy as the diagnostic gold standard for PBD when dermoscopic findings are nonspecific.
