DP27: Maculopapular cutaneous mastocytosis mimicking seborrhoeic folliculitis

B.S.D.P. Keragala¹ and Thiagarajah Balamurugan²

¹Ashford and St Peter’s Hospitals NHS Foundation Trust, Chertsey, UK; and ²Royal Surrey NHS Foundation Trust, Guildford, UK

Maculopapular cutaneous mastocytosis (MPCM), formerly known as telangiectasia macularis eruptiva perstans (TMEP), is an uncommon form of cutaneous mastocytosis, accounting for < 1% of cases. Unlike other types of cutaneous mastocytosis, this is commonly seen in adults and reported to be associated with systemic involvement. Herein, we report a case of a 35-year-old white man from South Africa referred for a mildly itchy progressive rash over the trunk of 2 years’ duration. This had been widely investigated and managed as follicular eruption with long-term antibiotics in the past (lymecycline and doxycycline). As he had recently moved to the UK and had not experienced any improvement with antibiotics, a re-evaluation was carried out. He has also suffered from gastro-oesophageal reflux disease for the same duration and had been on long-term proton pump inhibitors, where repeated endoscopies revealed severe reflux disease. Examination revealed multiple tan, red–brown blanchable macules and papules distributed symmetrically on the trunk and proximal upper and lower limbs. His face was completely spared. As lesions were being examined with a dermatoscope, they started to become more prominent, redder and Darier sign could be appreciated, which raised the possibility of cutaneous mastocytosis. Urgent skin biopsies were carried out using lidocaine without adrenaline. Histology revealed a mild increase in basal keratinocyte pigmentation, mild perivascular lymphocytic infiltration and occasional eosinophils and mast cells. CD117 immunostaining showed a slight increase in superficial dermal mast cells vs. a control biopsy taken from uninvolved skin. Serum mast cell tryptase was at the upper limit of the normal range (10 μg L^–1). The rest of the investigation revealed deranged liver transaminases. He was started on fexofenadine 180 mg twice daily with topical mometasone furoate 0·1% cream, which resulted in a slight improvement. He is currently being evaluated for systemic involvement and awaiting bone marrow biopsies and imaging. Patients with mastocytosis can develop localized or systemic symptoms secondary to degranulation of the infiltrating mast cells. Pruritus, blistering, flushing, dyspnoea, dyspepsia and diarrhoea are the commonly reported symptoms. Gastrointestinal symptoms are second only to pruritus and seen in 60–80% of patients with systemic disease. This case report highlights the importance of re-evaluation, a high degree of clinical suspicion and clinicopathological correlation in arriving at a diagnosis of a rare skin disease with variable presentations as they are often misdiagnosed and underdiagnosed.