MIXED CONNECTIVE TISSUE DISEASE
Priyankar Pal*
Asst. Professor, Pediatrics, Institute Of Child Health, Kolkata.*
Thirty five years have passed since 1972 when Sharp and colleagues (1) first proposed MCTD in 25 adults as a separate auto-immune disease. The syndrome included clinical features of rheumatoid arthritis, scleroderma, SLE, and dermatomyositis in conjunction with a high antibody titer to ribonucleoprotein. Since then, several reports of pediatric MCTD have appeared that have described the features in more than 200 children. However, the diagnosis still remains controversial and the controversy further stems from the fact that the disease exhibits considerable clinical variation cross-sectionally and over time.

As the disease exhibits considerable clinical variation over time, it is important to know what MCTD look like at presentation. Raynaud's phenomenon (85%) and polyarthritis (57%)(3) are the most common manifestations at onset. Arthritis is often associated with rheumatoid factor seropositivity, erosive disease is uncommon but deformity may develop. Swollen fingers and hands are mentioned in only one series (4) as a presenting feature.

Initially alternative diagnosis like JIA, SLE,and myositis are made frequently. None of the patients had scleroderma at presentation.
Lab Investigations
The complete blood count may show leukopenia, thrombocytopenia,or hemolytic anaemia. Very high titres of ANA antibodies that demonstrate a speckled pattern is virtually universal. Anti RNP antibodies in high titre is the serologic hallmark of MCTD. Further investigations confirm that the most characteristic specificities of the anti-RNP antibodies were directed against a uridine rich (U1), small nuclear RNP complex - the U1 RNP. The presence of anti U1-70 kd is characteristic of MCTD.

Criteria for diagnosis of this enigmatic disease have been evaluated for adults but not for children. 3 sets of criteria have been postulated for diagnosing? Sharp (1972) criteria, Alarcon - Segovia/Villereal classification and Kasukawa criteria.

Kasukawa's criteria: All 3 of the following must be met for diagnosis:
  1. Raynaud's or swollen fingers or hands or both
  2. Anti- RNP antibody positivity
  3. At least one abnormal finding from 2 or more of the following categories:
    1. Signs or symptoms of SLE (polyarthritis, facial rash, serositis, lymphadenopathy, leukopenia, thrombocytopenia)
    2. Signs or symptoms of scleroderma (sclerodactyly, pulmonary fibrosis, vital capacity < 80% of normal, carbon monoxide diffusion < 70% of normal, decreased esophageal motility)
    3. Signs or symptoms of dermatomyositis (muscle weakness, elevated creatine kinase, EMG abnormalities)

Treatment
There is no specific treatment. Management is aimed at addressing specific signs and symptoms. Many children respond satisfactorily to low dose glucocorticoids, NSAID's, or hydroxychloroquine, or a combination of these medications. (5) Patients with severe myositis, or renal or visceral disease generally require high dose glucocorticoid, and sometimes cytotoxic drugs (cyclophosphamide). In addition, methotrexate, mycophenolate mofetil, azathioprine, cyclosporine, etanercept and infliximab have been used. Autologous stem - cell transplantation has been advocated for life threatening disease. (6)

The long term outcomes are varied and unpredictable. Fulminant sepsis is the major cause of death, but pulmonary hypertension is the most common disease - related cause of morbidity and mortality.
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