Clinical Features
Pemphigus foliaceus (p. foliaceus) is considerably more rare than p. vulgaris and although it most often affects the middle aged and elderly, it has a very variable age of onset, sometimes affecting younger adults and even, occasionally, children. Very exceptionally, maternal antibodies have been known to cross the placenta resulting in neonatal disease. In general, non-endemic p. foliaceus in children is relatively benign and of short duration.
The superficial blisters of p. follaceus are exceedingly fragile and thereforemuch less obvious; erosions and large leafy scales or crusts are often predominant. The lesions may remain localized to the scalp, face and trunk for many months or years, leading to a mistaken diagnosis of seborrheic dermatitis, seborrheic keratosis or even lupus erythematosus. Sometimes the eruption involvesthe entire surface of the body or produces a clinical resemblance to exfoliative dermatitis (erythroderma). Mucous membrane involvement is rare. Exceptionally, patients may present with localized disease, typically restricted to the face. P. foliaceus often has a much more benign course than p. vulgaris, although patients with severe disease, requiring corticosteroid and immunosuppressant therapy, still have an appreciable mortality.
Very occasionally, patients may develop p. foliaceus during or after a previous episode of p. vulgaris and vice versa. This is accompanied by an antigen shift.
In addition to idiopathic p. foliaceus, drug-induced variants, notably due to penicillamine, may also be encountered.
Pathogenesis and histological features
Like other variants of pemphigus, p. foliaceus is an immunologically mediated disease. Examination of perilesional skin by direct immunofluorescent techniques reveals in vivo-bound immunoglobulin (usually IgG) and often complement (C3) in the intercellular region of the epidermis. Abundant antigen in the follicular outer root sheath and germinal matrix may account for the marked scalp involvement typical of pemphigus.
Indirect immunofluorescent techniques show that the sera of patients with p. foliaceus contain an IgG antibody that reacts with the intercellular region of normal squamous epithelium. IgG4 predominates followed by IgG1. IgG3 is also sometimes prescrit. This may be of importance since IgG3 is the most efficient activator of complement. Some 60-70% of patients are positive with indirect immunofluorescence.
The p. foliaceus antibody binds to a 160 kD desmosomal cadherin, designated desmoglein 1 (Dsg1). The sera of p. foliaceus patients bind to the extracellular aminoterminal domain of bovine Dsg1 whereas sera from both p. vulgaris and p. vegetans patients react with the intracellular domain of Dsg1. Compared with p. vulgaris, immunofluorescence studies on the sera of p. foliaceus tend to show more staining in the superficial epidermis, correlating with the level of the split. Conversely, the sera from patients with p. vulgaris show more affinity for the lower epidermis. Anti-Dsg1 antibody is pathogenic. Injection of purified anti-Dsg1 antibodies from sera of patients with p. foliaceus into neonatal mice induces subcorneal acantholysis in a pattern typical of p. foliaceus. The use of D-penicillamine may be associated with the acquisition of a pemphigus-like antibody and the development of p. foliaceus.
Since the blisters of p. foliaceus are superficial, they are therefore fragile and are often very difficult to obtain an intact lesion for diagnosis. Patients commonly have erosions without blisters, and frequently the clinician does not suspect a bullous disorder. Usually the cleft or blister lies within the granular layer or beneath the stratum corneum . The roof of the fragile blister is often not present, having sloughed either before or after biopsy. Acantholysis is frequently difficult to detect, but usually a few acantholytic cells can be found attached to the roof or floor of the blister. In those cases where the blister is missing, a careful inspection of the hair follicles may reveal focal acantholysis. Sometimes the blister contains numerous acute inflammatory cells, particularly neutrophils, which can make distinction from subcorneal pustular disorders especially difficult. Eosinophilic spongiosis may also be seen.
Differential diagnosis
The histological features in the superficial forms of pemphigus may be easily overlooked and, since bullae are often not appreciated by the clinician, the unwary pathologist may not consider a bullous disorder when evaluating the biopsy. A high index of suspicion is therefore critical. The differential diagnosis of superficial pemphigus includes IgA pemphigus, Subcorneal pustular dermatosis , Pustular psoriasis, Reiter’s syndrome, Pustular drug reaction, Bullous impetigo, Staphylococcal scalded skin syndrome, Pustular fungal infection. Distinction depends upon a careful consideration of the clinical information, the results of bacterial culture and immunofluorescent studies.
dans votre navigateur 
