Analysis of features associated with equivocal diagnosis and diagnostic discordance of Spitz naevi over an 18-year period.

BACKGROUND: Distinguishing Spitz naevi from malignant melanoma can pose diagnostic dilemmas and atypical subtypes present particular challenges to both clinicians and pathologists.

OBJECTIVES: We aimed to review our institutional experience of Spitz naevi, to characterise demographics and analyse the clinical and histological features associated with difficult/equivocal diagnosis of such lesions. Additionally we evaluated discordant cases following expert opinion at a second institution.

MATERIALS & METHODS: Data was retrospectively analysed on all cases of Spitz naevi treated over an 18-year period (1991-2009). Equivocal cases, (where a diagnosis of classical Spitz naevi could not be confidently made) were identified. The original/provisional diagnosis and second histopathological opinions were compared.

RESULTS: 148 cases were identified 112 lesions were classical Spitz naevi. 36 lesions (24.3%) posed diagnostic difficulty (equivocal cases). These equivocal cases tended to occur in the lower limbs, have brown pigmentation, be smaller in size (<6mm) and occur in older (>24 years) patients. Clinical sub-types and gender were not associated with equivocal cases. Of the 36 equivocal cases, the second opinion in 23 cases (63.9%) concurred with the original diagnosis. Of the remaining 13 cases (discordant cases), 10 cases that were originally deemed malignant were reported as benign after the second opinion. Two benign lesions were reclassified as malignant.

CONCLUSION: A firm histological diagnosis of Spitz naevi cannot be made with certainty in nearly a quarter of cases. Thus, additional external analysis for a second opinion should be sought for these equivocal cases.