Pigmented lesion on nail bed: Pseudo-Hutchinson sign

DIFFERENTIAL DIAGNOSIS OF THE PSEUDO-HUTCHINSON SIGN

The Hutchinson nail sign, first described in 1886, is a periungual band of brown-black pigmentation extending from the nail matrix onto the surrounding tissue, usually due to progression of subungual melanoma.¹ Pseudo-Hutchinson sign mimics Hutchinson sign but reflects a benign disease process. It is a diagnosis of exclusion, made only after malignancy is ruled out.²

Conditions associated with pseudo-Hutchinson sign include Bowen disease, subungual squamous cell carcinoma, fungal infection, ethnic (racial) melanonychia, Peutz-Jeghers syndrome, Laugier-Hunziker syndrome, systemic disease (systemic lupus erythematosus, scleroderma), radiation therapy, AIDS, congenital nevus, drug-induced dyschromia, malnutrition, chronic trauma, and subungual hematoma.^2,3

ASSESSMENT OF NAIL BED DISCOLORATION

Assessment of a pigmented nail bed lesion should begin with a complete history of the lesion including duration, color changes, and trauma, as well as a medical history that includes medication use and a family history of melanoma. Factors that should prompt investigation for melanoma include linear band widths greater than 3 mm, linear bands wider proximally than distally, heterogeneous nail discoloration, irregular border of the discloration, nail plate dystrophy or ulceration and bleeding, or involvement of high-risk digits (ie, thumb, index finger, great toe). However, malignancy should not be ruled out based solely on the history and physical examination. Other methods such as dermatoscopy can be used.

Dermatoscopy is a principal tool for clinical assessment of skin lesions and should be used routinely for all skin lesions. Studies have shown that compared with examination with the naked eye, dermatoscopy increases the diagnostic accuracy of melanoma.⁴ Whereas a linear brushy pattern indicates a benign condition, a diffuse haphazard pattern suggests malignancy.⁵ For suspicious lesions, serial monitoring (every 2 to 3 months), biopsy (especially excision of the pigmented lesion), referral to a dermatologist, and a second look by an expert pathologist are highly recommended. Although biopsy even in skilled hands can lead to nail dystrophy, the risk does not outweigh the risk of failing to diagnose a malignant condition such as acral melanoma.

DISCLOSURES

The authors report no relevant financial relationships which, in the context of their contributions, could be perceived as a potential conflict of interest.