The Papulonecrotic Differential Diagnosis

1. PLEVA (pictured here)

2. Lymphomatoid papulosis

3. Papulonecrotic tuberculid ( a rare form of cutaneous tuberculosis)

4. Arthopod assault

This is an important picture, in that the papulonecrotic ddx should roll off your tongue just as easily as ROYGBIV.  This is one of the fundamental descriptors in dermatology.  Congrats to those who got it right!

Staphylococcal impetigo

Impetigo can be caused by either staph or strep (GABHS) but these days, more is caused by staph than strep.  Bullous impetigo is mostly a newborn disease, and this is clearly not a newborn.  If it were staph scalded skin syndrome, it would be caused by two different exotoxins, which are generated by both a chromosomal process as well as a plasmid-generated process.

Since nearly everyone got this, I will not belabor the diagnostic cues.  

Graves' Disease

Graves' Disease is a veritable treasure trove for dermatologic signs and symptoms.  So many of the signs the old dermatologists and internal medicine docs used to look for are now obviated by routine thyroid panels, well before the thyroid disease declares itself by hair loss, hyperhidrosis, melanoderma, Plummer's nails or the like.  In other words, the lab rats are stealing our thunder!  

Pretibial myxedema occurs in roughly 4% of cases, presumably due to thyroid stimulating antibodies which also trigger production of glycosaminoglycans pretibially, preradially and retroorbitally.  The female to male ratio is 7:1.  Bonus q:  is Graves' Disease associated with hyper or hypothyroidism?  

Post Streptococcal Erythema Nodosum 

Erythema (red) Nodosum (painful) is an inflammation of the subcutaneous fat, and is triggered by a variety of circumstances, but most of them involve immune complexes being deposited in the medium sized vessels of the septae of the panniculus.  

The appearance is of a slightly elevated erythematous plaque often with, as you see above, a "vascular steal" phenomenon.  They are, as the name implies, very tender.  The location as well as the multiplicity and the tenderness all are clues as to its identity.

Most cases occur in young adult females, are usually multiple, usually pretibial and can be associated with other symptomatology associated with immune complexes such as joint pain, fever, headache and malaise.  Ulceration does not occur and they heal without scarring.  

Historically, tuberculosis was the most common associated disease, but currently we see it most commonly in association with  streptococcal disease, particularly pharyngitis.  Of course, it can also be associated with gut pathogens such as Yersinia, Salmonella and Shigella; but also a kazillion other infectious diseases (too numerous to be listed here) and also, of course, Sarcoidosis.  However, for two additional points, name two deep fungal diseases that cause EN. Also, the estrogens in oral contraceptives can trigger this condition, as can other meds such as sulfonamides.  

Eczema Herpeticum

Eczema herpeticum is a condition wherein the patient has a preexisting condition such as atopic dermatitis, and then suffers a herpetic outbreak, which subsequently seeds the inflamed, eroded skin with HSV.  This is such a case.  

This patient originally had a herpetic outbreak on the lips, which then quickly generalized to nearly all his skin.  Luckily, he was immunocompetent, otherwise this would have killed him.  He did very well on systemic (IV) Acyclovir.  

The clues to the diagnosis are history, especially the perioral history with the spread like wildfire, and also the primary lesions, which are vesiculopustular.  

Also known as Kaposi's Varicelliform Eruption, eczema herpeticum is a devastating disease that can be life threatening if not treated promptly.  The take home message is this, though:  In a patient with a chronic inflammatory condition such as atopic dermatitis or Darier's, if they also have a history of heprpes labialis (or genitalis) please ensure they are prophylaxed so as not to end up with the disseminated variety of their condition.

Incontinentia Pigmenti

IP is an X-linked Dominant genodermatosis noted by abnormalities in multiple organ systems.  It got its name from the whorled, irregular distribution of pigment in Blaschko's lines.  It is almost exclusively represented in females, being considered commonly a fatal mutation in males, with the exception of XXY Klinefelter's Syndrome males.  It is considered one of the ectodermal dysplasias, and thus will have many of the manifestations of ectodermal dysplasias.  Weirdly, they have a defective X-inactivation system, which causes both normal genetic expression and mutated genetic expression to occur at the same time in the same individual.

The lesions begin as vesiculobullous lesions, progress to verrucous linear and whorled plaques, progress to hyperpigmentation and then eventually they fade, often to hypopigmentation and atrophy.  Occasionally, these women may not know the diagnosis, and with the extremely subtle findings of some IP adult patients, the only clue may be multiple spontaneous abortions (presumably of male babies). 

As with many ectodermal dysplasias, they can have associated hair, nail, ocular or dental abnormalities, as well as neurologic abnormalities including seizures and mental retardation.

In contradistinction to the group of epidermal nevus syndromes, the lesions of IP are more swirled, and instead of being raised they tend to be flat or atrophic.

Superficial Spreading Melanoma with Signs of Regression

Try to imagine what this lesion would look like clinically.  What you see is scattered nests and individual melanocytes which have a "dusty (finely granular) cytoplasm, enlarged blood vessels and some evidence of regression in that you can see clumps of melanin in the superficial dermis.  There is superficial perivascular inflammation as well.  How does this translate to the naked eye?

The scattered melanocytes mean that the edge of the lesion will be more diffuse and hazy rather than clear cut, because the usual well-defined melanocytic lesion has nests of cells, rather than individual cells of pigment production at the edge.  

The pigment incontinence gives it a very, very dark appearance, often jet black, because of the depth of the pigment.  This pigmentary incontinence comes from the lesion being attacked by the immune system, which in turn causes the pigment in the melanocytes to leak out into the dermis.  

The enlarged blood vessels give it a slightly pinkish look at the periphery, and that, along with the inflammatory cells, makes it look slightly edematous.

I gave credit for any answer which involved melanoma, because it was a very subtle call between SSMM and MIS with regression.