Case 18 Female, 21 years. Hyperkeratotic pigmented papule, skin of legShow diagnosis & comments
Spitz naevus. Kamino bodies
(PREDOMINANTLY SPINDLE CELL) SPITZ NAEVUS
- Occurs at all ages, predominantly in children, adolescents and young adults
- Spindle cell type is the most common Spitz naevus subtype in adolescents and adults
- Spindle cell spitz naevi in that age group are most common on extremities
- May be junctional, compound or intradermal
- Junction component, if present, usually forms vertical oval nests; Confluence of nests may result in iregular masses
- Usually, there are shrinkage artifacts surrounding junctional nests, and, to a lesser extent, between cells within the same junctional nest.
- When a junctional component is present, there is usually epidermal hyperplasia
- Transepidermal elimination of nests and some ascent of solitary cells may be seen.
- Ascending cells are commonly smaller than junctional ones
- Dermal component often forms nests in the upper central part, but smaller cell groups and individually dispersed cells in the periphery, including the lesional base
- Towards the base (and lateral periphery) intradermal cells become progressively smaller
Mitotic figures are usually uncommon and tend to be limited to upper parts of the lesion
Overall, the architecture is regular (cellular features, arrangement of cells, type and degree of reactive changes). No abrupt changes in cell type or lesional architecture
Pigment is often absent or scarce, but some examples contain more pigment.
These are solitary rounded or confluent, amorphous, eosinophilic masses of basement membrane material, found at the dermoepidermal junction, most commonly at the tips of dermal papillae, in some Spitz naevi and, far less commonly, other benign and malignant melanocytic proliferations.
Clusters of Kamino bodies are so much more common in Spitz naevi than in other lesions, that they form an important diagnostic clue. However, their presence does not rule out melanoma completely, since a rare melanoma contains similar clustered Kamino bodies. In H&E sections, Kamino bodies show some resemblance to Civatte bodies, as can be found in lichen planus, but the letter represent apoptotic cell remnants, whereas Kamino bodies consist of extracellular matrix components.