LAUSR

A 15-year-old male, with personal history of limb-girdle muscular dystrophy, was admitted to the paediatric ward for a 1-month history of pruritic, generalised, polymorphous eruption and severe painful mucositis. Two months earlier he had been diagnosed with SARS-CoV-2-induced mucositis and treated with prednisolone 40 mg/day for 2 weeks with improvement. At home, due to further therapeutic non-compliance by the patient, mucous lesions recurred associated with a de novo skin eruption, leading him to the emergency department and subsequent hospitalisation. Physical examination revealed shiny, erythematous, flat-toped papules, scarce tense blisters and erosions, scattered over the trunk and extremities, sparing the face. There were multiple palmoplantar blisters and peri-ungual erythema, erosions and crusts. There were widespread erosions of the oral mucosa extending to the vermillion, where there were also pseudomembranes and haemorrhagic crusts (Fig. 1). The glans penis and conjunctiva showed erosions and hyperaemia, respectively. Nikolsky sign was negative. Neither lymphadenopathy nor organomegaly was noticed. Biopsy of a blister demonstrated foci of acantholysis in the mid and superficial epidermis and vacuolization of the basal layer with few apoptotic keratinocytes (Fig. 2). In the superficial dermis, there was moderate perivascular lymphocytic infiltrate. Direct immunofluorescence of perilesional skin revealed intercellular deposition of immunoglobulin G (IgG) and C3. Immunoprecipitation showed anti-desmoglein-3 and antidesmoglein-1 antibodies. Clinical, histological and immunofluorescence findings established the diagnosis of paraneoplastic pemphigus (PNP). The patient started methylprednisolone 80 mg/day (1 mg/kg/day). Further investigation, including complete blood count, renal and liver functions, protein electrophoresis and anti-nuclear antibodies, was unremarkable. Normal serologies for herpes simplex virus and Mycoplasma pneumoniae, ruled out other possible causes of mucositis. Positron emission tomography/computed tomography (PET/CT) showed multiple retroperitoneal lymphadenopathies and a 62 105 118 mm hypermetabolic, lobulated mass (Fig. 3), of which biopsies were inconclusive, exhibiting inflammatory infiltrate alone. During this time, due to lack of improvement with corticosteroid therapy alone, azathioprine 50 mg/day was added and an eight-session treatment with plasmapheresis was performed. Following this, the patient underwent incomplete resection of the tumour, whose histologic examination revealed a hyaline vascular variant of Castleman’s disease. Given the involvement of multiple lymph nodes, the patient was diagnosed with multicentric Castleman’s disease. Considerable improvement over the first month following surgery allowed a reduction of methylprednisolone to 16 mg/day. Since a second procedure to remove the remaining tumour was not feasible, and the patient still had few painful skin lesions with significant mucositis, he started monthly cycles of intravenous immunoglobulin (IVIg) 1 g/kg. During the next 6 months, he showed global improvement of the dermatosis (Fig. 4), despite maintaining refractory oral mucositis. Currently, he is being treated with methylprednisolone 16 mg/day, azathioprine 100 mg/day and monthly IVIg, showing stable disease, but recurrent infectious complications requiring hospitalisation and multiple antibiotic regimens. He has now completed 10 months of follow-up.