RNP positive antibodies and paediatric-onset mixed connective tissue disease

Abstract

Aim Mixed connective tissue disease (MCTD) remains a poorly defined entity at all ages. The hallmark of the various proposed diagnostic criteria is the presence of anti-U1-ribonucleoprotein (RNP) antibodies together with characteristic clinical features which include Raynaud9s, myositis, arthritis and swollen fingers. There is limited clinical or epidemiological data on MCTD specific to children. The authors describe six children with a clinical diagnosis of MCTD currently attending paediatric rheumatology clinics within the Scottish Managed Clinical Network for Paediatric and Adolescent Rheumatology serving a childhood population of 1.03 million. Methods Case notes were reviewed of all known current RNP positive antibody patients, presenting to paediatric rheumatology before their 16th birthday with features suggestive of a diagnosis of MCTD. The childhood population of Scotland was estimated from the office of national statistics. Results Six children were identified with positive RNP antibodies and clinical features compatible with a diagnosis of MCTD. Five were female, one male. Mean age at diagnosis was 10.8 years (range 8–15 years). Four of the six cases had Raynaud9s; in three, this was the initial symptom. Of the other two cases, one had uniphasic colour (blue) changes of the fingers, the other significant swollen fingers. During the course of their disease all had significant arthritis, five had myositis and five had sclerodermatous skin changes. One child had recurrent parotid swelling. One child had panniculitis skin lesions. All were treated with steroids (oral +/− intravenous) plus methotrexate. Four patients responded well, with significant improvement in their clinical state. One child failed to respond and was treated successfully with mycophenolate mofetil. The sixth responded poorly to steroids and methotrexate and was commenced on infliximab, which was discontinued when they developed Hodgkin9s lymphoma. Other complications of the disease and its treatment in this group included poor growth in two; severe joint damage in three; erosive oesophagitis in one and deafness in one. Conclusions The diagnosis of MCTD in a paediatric population remains difficult. Clinical features in this group were varied and not all presented classically with Raynaud9s. This cohort may therefore underestimate the paediatric population prevalence of MCTD, which we have approximated at 6 per million.