Integration: Unifying Concept
Clinically and histopathologically, Mucha-Habermann disease is a single distinctive pathologic process. It is not unique in being associated with lesions that may be accelerated to become blisters or decelerated to remain scaly papules. The same is true of lichen planus, which may become vesicular (bullous lichen planus) or be scaly papules, of psoriasis, which may become pustular (pustular psoriasis) or be scaly papules or plaques, and of lupus erythematosus (lupus dermatitis), which may be bullous (bullous lupus erythematosus) or simply scaly papules and plaques.
Papules of pityriasis lichenoides acuta are characterized histopathologically by a wedge-shaped, superficial and deep, perivascular infiltrate of lymphocytes, and by lymphocytes scattered along the dermoepidermal junction in association with vacuolar alteration. Individual necrotic keratocytes are present throughout an epidermis that displays ballooning and spongiosis. Parakeratosis that may house neutrophils is also present. If extravasated erythrocytes are numerous, the lesions will be purpuric. If ballooning and spongiosis eventuate in vesiculation, a papulovesicle is the result. When epidermal necrosis is extensive and ulceration supervenes, an eschar comes into being. If ulceration is deep enough, a scar results.
Pityriasis lichenoides chronica is typified histopathologically by a superficial perivascular infiltrate of lymphocytes, lymphocytes in association with vacuolar alteration along the dermoepidermal junction, only a few necrotic keratinocytes within the epidermis, just a hint, if that, of ballooning and spongiosis, and subtle mounds of parakeratosis. The lesions of this scaly clinical presentation never progress to vesiculation, ulceration, eschars, or scars.
Not surprisingly, some patients with pityriasis lichenoides show acute and chronic lesions concurrently. The fulminant expression of the process is simply a caricature of pityriasis lichenoides acuta.
Despite some similarities in the clinical appearance between Mucha-Habermann disease and lymphomatoid papulosis, the two are unrelated. Mucha-Habermann disease is an inflammatory process, whereas lymphomatoid papulosis is a lymphoma.