Objective The T-Spot.TB is an interferon-gamma release assay (IGRA) which is increasingly used in dermatology as a screen for latent TB before initiation of biologics and for confirming diagnosis of tuberculids. This study aims to explore its concordance with tuberculin skin tests (TST) and eventual diagnosis of latent TB. Study design This is a retrospective review of all patients in NSC who had a TB T-spot test done between 2008 and 2010. We looked at the dermatological diagnosis, results of T-Spot.TB and TST, chest radiograph findings, tuberculosis status and treatment of TB. Result 51 TB T spot tests were ordered in National Skin Centre between 1 January 2008 and 9 June 2010. 31 tests were for patients with psoriasis with the intention of initiating biologics; 5 were for patients with suspected tuberculids and tuberculosis verrucosa cutis; 3 were done as part of work-up for possible erythema nodosum; 3 tests were part of screening for latent TB in hospital staff and 9 tests were performed for other reasons. There were a total of 13 patients eventually diagnosed with latent or active TB infection. All of whom had a positive T-Spot.TB result except for 1 patient with an indeterminate result. On the other hand, out of these 13 patients, only 5 showed a positive TST, 2 had negative TST and 4 patients did not have a TST done. There were a total of 14 positive T-Spot.TB results for which 12 eventually received antituberculous therapy. All patients with erythema induratum had a positive test result. Six patients’ T-Spot.TB tests were borderline, indeterminate or could not be interpreted due to insufficient lymphocyte yield. Conclusion Our study shows the utility of T-Spot. TB test in various conditions seen in dermatology clinics in a local setting. We suggest that the T-spot test can supplant the tuberculin skin test in screening latent TB for psoriasis patients for whom biologics are intended and in erythema induratum. The high incidence of borderline and indeterminate results should not be ignored. This should be taken into account when interpreting the IGRA especially if patients are on immunosuppressive therapy.

Introduction: Lichen planus pemphigoides (LPP) is a rare acquired autoimmune disease characterised by the evolution of subepidermal blisters on normal and lichen planus affected skin. Case summary: We describe a case of lichen planus pemphigoides in a 54-year-old Chinese woman. The patient presented initially with scaly psoriasiform plaques and was diagnosed to have guttate psoriasis. She was treated with narrowband ultraviolet (NBUVB) therapy twice weekly. Within a month of starting phototherapy, she experienced a flare up of her skin lesions with a generalised eruption of violaceous papules, tense bullae over the lower limbs as well as Wickham’s striae over the buccal mucosa. Histology of the violaceous papule over abdomen revealed interface dermatitis, while the specimen from a blister showed subepidermal bulla with linear deposition of IgG and C3 along the basement membrane zone. A diagnosis of LPP was made on clinicopathological grounds. The patient subsequently responded well to oral prednisolone at a dose of 0.5 mg/kg/day. Conclusion: This is the first case report of NBUVB alone unmasking LPP. In the presentation, we will describe the pathological mechanism of NBUVB in the development of LPP and the key features distinguishing LPP from bullous lichen planus (BLP), psoriasis and bullous pemphigoid (BP).