Pemphigus Vulgaris - A Dermatological Red Herring
You’re eating really spicy meat on a sunny, Sunday afternoon. The second bite you take off your meal, your mouth hurts like you’ve bitten it, but you really haven’t. So all your evening plans are changed now, and you book an appointment at your clinic. One look at the inside of your mouth and your doctor comes to the conclusion that it’s an apthous ulcer. And here in lies one of the biggest misconceptions of medicine. Pemphigus vulgaris is most commonly mistaken for idiopathic apthous ulcers.
Pemphigus Vulgaris is an auto-immune skin disorder which results in oozing blisters, in the buccal mucosa, the skin and even the genital organs. Let’s recall the structure of the skin. It’s divided into three layers, the outer, epidermis, the middle, dermis and the inner, hypodermis. The epidermis is firmly connected to the dermis by a basement membrane. All the keratinocytes (squamous cells) in the epidermis are adhered to each other by intracellular connections called desmosomes and hemi-desmosomes.
In pemphigus vulgaris, the immune system produces auto-antibodies against the desmosomes in the BMZ (Basal Membrane Zone) of the epidermis, particularly, against desmoglein 1 and desmogelin 3. It’s a type II hypersensitivity reaction as the body forms antibody-antigen complexes in the tissues of the body.
Essentially these antigen-antibody complexes disrupt the skin by sloughing off the entire epidermal layer but leaving the basal cells intact with the basement membrane. These basal cells show a characteristic tomb-stone appearance.
Once, the epidermal layer is detached from the basal cells in the basement membrane, transduative fluid fills the gap between them. This fluid forms inside a thin vesicle, called the bulla. This thin vesicle which contains the transduative fluid bulges through the epidermis and to the external surface which can be broken easily and thus producing an oozing skin lesion. Formation and breaking of one bulla is negligible but in pemphigus Vulgaris, auto-immune attacks on thousands of desmosomes produces skin lesions in the buccal mucosa, the skin excluding the palm and sole and the genital regions.
This image shows the space between the epidermal layer and the basal layer. The gap is a place where the transudative fluid collects.
Notice the tombstone appearance of the basal cells.
As we read in the beginning, Pemphigus Vulgaris is frequently misdiagnoised as apthous ulcers in the mouth. To differentiate these and also to differentiate Pemphigus Vulgaris from another auto-immune skin disorder called the Bullous Pemphigoid, (where the entire epidermal layer is detached from the dermal layer and the blisters occur sub-epidermally) we have to look for a clinical sign, called the Nikolsky’s sign. A shearing force on the skin, results in the exfoliation of the superficial layer of skin. This is positive in Pemphigus Vulgaris and negative in the other two.
Pemphigus Vulgaris, if diagnosed early, can be treated with topical formulation of corticosteroids, mainly glucocorticoids, like dexamethasone. This has an immune-suppressive action but also has varying side-effects in the long run. These include drug-induced Cushing’s syndrome, hypertension and even makes the patient susceptible to infectious diseases. Thus a newer alternative is rituximab, a monoclonal antibody which given along with IV immunoglobulin delays the recurrence of this disease to a maximum of 10 years. Even though this seems like the ideal drug for this auto-immune skin disorder it should be monitored frequently as it can activate any latent infections of the body.