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An 82-year-old healthy woman presented with bullae, partly hemorrhagic, on the trunk and extremities (Fig. 1), secreting erosions, and submammary macerations (Fig. 2). The blistering disease developed over a 2-year period, during which she reported taking no drugs. She did, however, begin using a food supplement containing the blue–green alga Spirulina platensis 1 year before the onset of the eruption.

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Figure 1. Hemorrhagic bullae on the extremities

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Figure 2. Submammary bullae, secreting erosions, and macerations

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 At admission, the Nikolsky sign was positive. The first biopsy showed a subepidermal bulla with a denuded surface and sparse perivascular lymphocytic infiltrate with scattered eosinophils (Fig. 3). The second biopsy, taken during admission, demonstrated an intra- and subcorneal vesicular dermatitis with slight superficial acantholysis. Direct immunofluorescence disclosed immunoglobulin G (IgG) and C3 at the dermoepidermal junction. Indirect immunofluorescence was also positive at the dermoepidermal junction. A salt split test demonstrated IgG, IgM, and C3 on the upper side of the bulla. Immunoblotting of the serum was negative and showed no pemphigoid or pemphigus antigens. Enzyme-linked immunosorbent assay (ELISA) for desmoglein 1 and 3 antibodies was also negative.

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Figure 3. The first biopsy showing subepidermal hemorrhagic bulla with denuded surface and sparse perivascular lymphocytic infiltrate with scattered eosinophils (hematoxylin and eosin, ×10)

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 Diagnostic investigations for neoplasia, Wood's lamp exposure of urine, purified protein derivative (PPD), and antinuclear antibody (ANA) were negative.

 With a diagnosis of mixed immunoblistering disorder exhibiting features of bullous pemphigoid and pemphigus foliaceus, prednisone 60 mg was started and gradually tapered, and topical treatment was begun with creams containing silver sulfadiazine and triamcinolone/neomycin. Suspecting the involvement of Spirulina in the disease, the food supplement was stopped. With this treatment, the patient steadily improved with no appearance of new blisters.

 An in vitro interferon-γ release test with the Spirulina-containing food supplement, conducted to explore the connection between the agent and the eruption, yielded a slight increase in interferon (19%). The result was considered to be borderline, but, in view of the clinical picture and the fact that the patient was being treated with 20 mg prednisone at the time, the test can be considered as positive.

 Three months after completion of the prednisone treatment, and with avoidance of the Spirulina-containing supplement, the patient was free of lesions with no recurrences.