Mucous membrane pemphigoid (MMP) encompasses a heterogeneous group of diseases, which predominantly affects the elderly. The peak incidence is at roughly 70 years. However, rare childhood cases have also been reported. There is no racial or ethnic predilection associated with MMP, but the condition does appear to be twice as common in women than it is in men. For completeness, MMP is also termed cicatricial pemphigoid, oral pemphigoid and ocular pemphigoid.
Clinical course and presentation
MMP is a chronic autoimmune disease that is recognized by sub-epithelial blistering lesions and eventual scarring of the mucous membranes, skin, or even both. Affected membranes may include the conjunctiva, oesophagus, trachea, nasopharynx, larynx, genitourinary tract, and anus. Of these, the most commonly affected are the oral mucosa and conjunctiva. In less common cases the skin may also be involved. 20-30% of cases present with blistering lesions found on the face, neck and scalp. Lesions of the skin may either be fluid-filled blisters (bullous) or reddish (erythematous) plaques, which may bleed or itch. Scarring may result in patches of discolored skin (hyperpigmentation or hypopigmentation) and areas of hair loss if the scalp is affected. Irrespective of the membrane(s) affected, MMP persists for a long time and remissions and recurrence are both frequent.
Clinical presentation tends to vary depending on the membrane(s) affected. Chronic inflammation, painful, persistent vesicles, erosion and the common resultant scarring of the mucous membranes may cause significant morbidity by leading to tissue destruction and functional shortcomings. For example, conjunctival scarring may contribute to blindness and gingival scarring and inflammation may result in the loss of teeth.
The exact cause of MMP is unknown. It is an autoimmune disorder (i.e. it occurs when the body produces autoantibodies against healthy ‘self’ tissue). In MMP, these produced autoantibodies react with target proteins (antigens) located in mucous membranes and skin tissue. More specifically,
the autoantibodies attack the basement membrane zone (BMZ) of the epithelium. The BMZ functions in holding the outer layer of skin onto the underlying tissues. Therefore, when the BMZ is attacked and destroyed by the autoantibodies, the skin is no longer anchored down, allowing it to become detached and produce blister. Immunological studies have revealed that the precise targets of these autoantibodies are antigens, which include BP180 and laminin 5. Other suggestions such as the subunits of the α6β4 integrins, Collagen VII and BP230 have also been postulated.
It has been suggested that affected individuals may have a genetic susceptibility to the development of some forms of MMP. The development of such cases would likely be multifactorial by requiring contribution of immunological, genetic, environmental, and several other factors.
It might also be the case that MMP is the unfortunate result of the use of certain drugs or following trauma to the affected area. For example, some cases of MMP predominantly affecting the eyes may become apparent following a form of ocular surgery such as cataract removal.
Treatment of MMP is in the form of symptomatic management. The symptoms can usually be controlled with the right single medication (or combinations) in order to keep the sores and blisters under control. Whilst it is fortunate that the likelihood of death is rare, the possibility of incurring morbidities such as blindness is serious enough to raise concern amongst sufferers.