The Interface vacuolar reaction pattern can give rise to epidermal changes but it is mainly through the process of keratinocyte destruction. Usually this is caused by lymphocytes invading the epidermis and directly destroying keratinocytes or where keratinocytes are collateral damage where the primary antigen is a drug attached to the keratinocyte. Usually there is associated vacuolar changes to the basal keratinocytes and so the interface pattern is divided into lichenoid and vacuolar pattern subtypes.
The main conditions showing vacuolar changes that significantly affect the epidermis are the following.
In erythema multiforme the typical lesions are the target lesions, where there is a surrounding area of erythema and a central area that is much darker. Sometimes this central area can be bullous, again a reflection of the degree of damage that is occurring to the epidermis at certain points.
Fixed drug reaction can also give rise to a bullous lesion usually with very little in the way of surrounding erythema but there is often post-inflammatory hyperpigmentation and this may be the feature with melanin melanophages which is most apparent histologically depending on the stage at which you are viewing the specimen.
Prominent interface damage at the dermal/epidermal junction with prominent vacuolar change to the basal keratinocytes and pink Civatte bodies or dyskeratotic cells throughout all levels of the epidermis indicate a more severe immunological challenge to the epidermis and this picture is typically seen in erythema multiforme and in fixed drug eruptions. In erythema multiforme the epidermal cell death can occur at all levels and there is often a marked infiltrate of the lymphocytes into the epidermis itself so that it is difficult to see the dermal/epidermal junction. Remember that in these circumstances with erythema multiforme, either secondary to a viral infection such as herpes simplex or a drug reaction, that the target cells are the keratinocytes themselves.
The main conditions showing vacuolar changes that significantly affect the epidermis are the following.
In erythema multiforme the typical lesions are the target lesions, where there is a surrounding area of erythema and a central area that is much darker. Sometimes this central area can be bullous, again a reflection of the degree of damage that is occurring to the epidermis at certain points.
Fixed drug reaction can also give rise to a bullous lesion usually with very little in the way of surrounding erythema but there is often post-inflammatory hyperpigmentation and this may be the feature with melanin melanophages which is most apparent histologically depending on the stage at which you are viewing the specimen.
This idea of lesions having lives was one put forward by Bernard Ackerman and basically it means that the pathological process varies depending on the stage of the illness and the stage of development of the lesion that is being examined.
Prominent interface damage at the dermal/epidermal junction with prominent vacuolar change to the basal keratinocytes and pink Civatte bodies or dyskeratotic cells throughout all levels of the epidermis indicate a more severe immunological challenge to the epidermis and this picture is typically seen in erythema multiforme and in fixed drug eruptions. In erythema multiforme the epidermal cell death can occur at all levels and there is often a marked infiltrate of the lymphocytes into the epidermis itself so that it is difficult to see the dermal/epidermal junction. Remember that in these circumstances with erythema multiforme, either secondary to a viral infection such as herpes simplex or a drug reaction, that the target cells are the keratinocytes themselves.
A fixed drug reaction has a very similar picture, again for the same immunological reasons, but here the drug is probably attached to a keratinocytic protein and is acting as a hapten and it is a Type 2 immune reaction that can give very extensive damage to the epidermis. If it is extensive enough you will actually get blisters. Otherwise you can almost get complete necrosis of the epidermis and the latter is a feature of the condition toxic epidermal necrolysis where not just localised areas as in fixed drug but generalised areas of the skin can be subject to this immunological attack. In a fixed drug, depending on the stage at which it is biopsied, you may see a lot less of this vacuolar change at the dermal/epidermal junction and more melanin continence with melanin in melanophages. The prominence of eosinophils in this area of infiltrate is much more in favour of a fixed drug eruption.
Graft versus host disease is also a lichenoid infiltrate but it is often much more sparse than in lichen planus and again, though there can be significant vacuolar damage at the dermal/epidermal junction, it is seldom full thickness. It is similar to a mild form of erythema multiforme and it may show the phenomenon of what is called satellite cell necrosis where you have a lymphocyte next to a dead keratinocyte.
Lupus erythematosis can give both a lichenoid and an interface vacuolar pattern and the degree of one or the other determines to some extent the clinical appearance. The three major clinical variants of lupus are discoid lupus, subacute lupus and systemic lupus. In discoid lupus a lot of the damage is centred round hair follicles, also at the dermal/epidermal junction and with a superficial and deep perivascular infiltrate in the dermis. There is often thickening of the basement membrane and a few scattered Civatte bodies or dyskeratotic cells. A degree of hyperkeratosis and follicular plugging is also seen.
In subacute lupus you have much more damage at the dermal/epidermal junction with basal vacuolar change and you may in fact get epidermal atrophy. There can be a bit of mucin also in the dermis in conjunction with thickening of the dermal/epidermal junction. In a condition called tumid lupus there is even more mucin in the dermis but there is not as much epidermal involvement and there is still a superficial and deep perivascular infiltrate.
In systemic lupus you have much more basal vacuolar damage but the infiltrate of lymphocytes can be a lot less than you might expect. The damage is more centred on the keratinocytes in the epidermis itself and you may also see sub papillary oedema and extensive mucin in the dermis. There are usually much fewer dyskeratotic cells in the epidermis, so there is less epidermal reactivity and hence less epidermal scaling and the like. Typically systemic lupus shows mainly skin erythema. There is also sometimes vascular damage with fibrin in the blood vessels.
In lupus panniculitis the main area of damage is in the fat layer and here you have a lobular panniculitis with lymphocytes invading and destroying the fat lobules. There may be some overlying epidermal changes of discoid lupus as well.
Bullous lupus will have a subepidermal blister and surprisingly there are often neutrophils in the dermal papillae with lymphocytes in the perivascular area, but this is a rare condition.
In subacute lupus you have much more damage at the dermal/epidermal junction with basal vacuolar change and you may in fact get epidermal atrophy. There can be a bit of mucin also in the dermis in conjunction with thickening of the dermal/epidermal junction. In a condition called tumid lupus there is even more mucin in the dermis but there is not as much epidermal involvement and there is still a superficial and deep perivascular infiltrate.
In systemic lupus you have much more basal vacuolar damage but the infiltrate of lymphocytes can be a lot less than you might expect. The damage is more centred on the keratinocytes in the epidermis itself and you may also see sub papillary oedema and extensive mucin in the dermis. There are usually much fewer dyskeratotic cells in the epidermis, so there is less epidermal reactivity and hence less epidermal scaling and the like. Typically systemic lupus shows mainly skin erythema. There is also sometimes vascular damage with fibrin in the blood vessels.
In lupus panniculitis the main area of damage is in the fat layer and here you have a lobular panniculitis with lymphocytes invading and destroying the fat lobules. There may be some overlying epidermal changes of discoid lupus as well.
Bullous lupus will have a subepidermal blister and surprisingly there are often neutrophils in the dermal papillae with lymphocytes in the perivascular area, but this is a rare condition.
The other collagen diseases such as dermatomyositis are similar to lupus, more perhaps to the subacute lupus variant than any of the others. The perivascular infiltrate is usually superficial rather than superficial and deep and the degree of basal vacuolar damage is not as great, neither is the amount of mucin that is deposited in the dermis. However there may be a little bit more epidermal atrophy than you will see in some cases of lupus.
The only other lichenoid interface condition that perhaps we should mention is lichen sclerosus et atrophicus. Again it depends on the stage of the illness that is biopsied. In the late stage there will be quite marked collagen deposition in the upper dermis and this band of collagen is quite a prominent feature. It is usually relatively acellular and there is usually atrophy of the overlying epidermis. Of course if you see this at an earlier stage there may be a more superficial dermal infiltrate of lymphocytes with perivascular prominence and damage to the basal layer. The sclerotic changes only occur as a later feature. There also may be follicular plugging in this condition, again because of the early epidermal involvement. Sometimes bleeding is also seen.
