Case Number : Case 848 - 17th September Posted By: Guest

There is a prominent discrepancy between the H&E-stained histology (which does not show extensive melanocytic proliferation) and the Melan A (which appears to stain many cells); therefore one should wonder whether he is dealing with overstained keratinocytes (or more correctly stated picked up by keratinocytes). MITF, being a nuclear stain, may resolve this dilemma. I favor a non-malignant pigmented process.

Agree. Would be nice to see additional melanocytic markers or dual staining to clarify if this is predominantly keratinocyte staining with Melan-A (favoured), although no doubt some of the crisper staining does appear to relate to dendritic melanocytes, versus genuine melanocytic increase.

Clinical description will definitely help noting the [b]size, colour, border, any surface changes and any skin markings alterations[/b] preferably with the use of dermatoscope. There is [b]basal hyperpigmentation[/b]. [b]Melanocyte number seems to be increased[/b] (but [b]Melan-A can recognise the antigen transferred from melanocytes to keratinocytes[/b]). The papillary dermis contains a sparse [b]lymphoid infiltrate, solar elastosis and scattered melanophages[/b]. Lentigo is a possibility. Lentigo is a risk factor for skin cancer and sunburn. Lentiginous melanoma is another possibility.

Quite a tricky one.....waiting to be enlightened.

Same as Sasi, feeling confused, waiting to be enlightened!!!!

[i]This case looks familiar! There is a website glitch where there are two cases labeled #847 from yesterday....today's case is partially copied there as the first of the two cases #847 (with fewer immunostain images). I will copy over my opinions from that earlier case, to here...[/i]

[quote name='Jim Davie MD' timestamp='1379372689']
I favor lentigo simplex.

Although there is marked solar elastosis, the junctional melanocytes appear cytologically bland (no enlargement, pleomorphism, hyperchromatism, angulated nuclear/cytoplasmic contours, or 'starburst' multinucleated giant cells). No significant architectural atypia is present (neither high level intraepidermal pagetoid scatter, nor downward pagetoid spread along eccrine or follicular adnexa on Melan-A immunostain; there is no lentiginous confluence, and no irregular junctional nesting at least in the images provided). This biopsy shows heavy melanin in basal keratinocytes and in stratum corneum, which I imagine might clinically correspond with an 'inkspot lentigo' or dark macule.
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[quote name='Jim Davie MD' timestamp='1379430098']
I find the use of Giemsa counterstain (in place of hematoxylin counterstain) invaluable when using DAB (brown chromogen) immunohistochemistry on pigmented lesions; I find it a [b]much [/b]preferred alternative to melanin bleaching.
Melanin granules will stain a distinct dark green-brown, whereas DAB is a pure brown; this makes identification of melanophages and pigmented keratinocytes much easier, and does not suffer the cytology-obscuring, overstaining artefact often seen when using ACE (red) chromogen as an alternative to DAB (brown). This makes it easy to see both melanin granules and positive DAB staining in the same cells. [Not to mention, DAB is more durable than ACE over the years.]
[/quote]

As usual Jim pretty much read my own thought processes! I was thinking of a lesion akin to dark flat solar lentigo or ink-spot lentigo-like pigmented macular lesion. I don't see any increase in melanocytes on the H&E's (so did not go for a simple lentigine / lentigo simplex) and presumed the IHC is mainly DAB but spuriously expressed in the keratinocytes. Will give Jim's suggestion a try in future but I usually find a very thin good quality H&E is preferable to melanin bleach (or IHC) in any case for darkly pigmented lesions.

I think there's no melanocytic proliferation, but just epidermic hyperpigmentation characterized by alternating areas of heavy hyperpigmented keratinocytes and areas of light hyperpigmented keratinocytes, what may impart a reticulate appearance to the lesion on clinical examination. Following this line of reasoning, I could think of late Kitamura's reticulate acropigmentation or related disorders.
Aditional clinical information certainly will be helpful.

Weedon points out that [b]a subsequent excision[/b] may show more pronounced features than the original biopsy specimen. This is particularly so for lesions on actinically damaged skin, in which up to 40% of excisions may show more pronounced changes.

On a different note, I would like to thank Dr McKee for the extremely useful site he had. I have been an occasional visitor to the new DermpathoPro site and I wish it the best.