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Mixed Connective Tissue Disease

Mixed Connective Tissue Disease (MCTD)

MCTD is a rare condition with overlapping features of more than one connective tissue disease, namely JSLE, systemic sclerosis, and polymyositis. It is more common in girls (3:1) with a median age at onset of 11 years. 

When to suspect MCTD: 

  • Raynauds phenomenon.
  • Prominent arthritis affecting hands (swollen / puffy fingers).
  • High titres of Anti-Nuclear Antibodies (ANAs) with a speckled pattern.
  • Skin changes including scleroderma-like disease; rashes of JSLE +/or JDM. Vasculitis can occur and be severe. 
  • Multisystem disease (Lung, gut, sicca syndrome) but absence of severe renal and central nervous system involvement
  • Pulmonary hypertension.

Clinical Manifestations

  • Features tend to develop sequentially, but not in any predictable order or timescale.
  • Polyarthritis (93%) and Raynauds phenomenon (85%) are most common at onset but many other features can occur and almost any organ can be involved.
  • The rashes of JSLE or JDM are common at onset. Sclerodermatous skin changes are slow to develop but may become the most prominent feature of the disease later.
  • Although children typically do not complain of shortness of breath, they often have pulmonary functional impairments. Pulmonary hypertension is the most frequent serious complication.
  • Moderately asymptomatic involvement, such as myositis with minimal weakness, atrophy, and minimal to moderate increases in the serum muscle enzyme concentrations, is common.
  • Other features may occur: Dysphagia and bowel dysmotility and Sicca syndrome (xerostomia, kerato-conjunctivitis sicca, or parotid gland enlargement in up to 1/3 of children). Autoimmune thyroid disease may also occur.

Laboratory features 

  • Autoantibodies
    • High titres Anti-Nuclear Antibodies (ANAs) with a speckled pattern.
    • Anti-U1 Ribonucleoprotein antibodies (Anti-RNP) antibodies often in high titre (but may be present in low titres in other diseases, such as JSLE).
    • Rheumatoid Factor is commonly seen.
    • Antiphospholipid antibodies may occur.
  • Anaemia, Leukopaenia, Thrombocytopenia, Hypocomplementemia. 
  • Elevated muscle enzymes. 
  • Hypergammaglobulinemia is commonly observed.
  • Abnormal Lung Function Tests suggestive of interstitual lung disease. 

Management 

There is no specific treatment for MCTD. Management should address the predominant problems such as arthritis, cutaneous disease, or visceral involvement. Evaluation for early internal organ involvement is needed. 

Course of the Disease and Prognosis

The long-term outcomes of MCTD are varied and unpredictable. Morbidity and mortality in MCTD are more often associated with development of pulmonary hypertension or gradually evolving restrictive pulmonary disease (15%) with minimal fibrosis. Pulmonary dysfunction may be underestimated clinically because it tends to develop insidiously. Another ominous development is severe thrombocytopenia (20%), which is often resistant to conventional therapy. This complication is more common in children than in adults. Disease activity correlated with increasing titre of anti-RNP and RF factors. Presence of RF at diagnosis predicted disease persistence.

The term Undifferentiated Connective Tissue Disease (UCTD) is often used to describe patients who have some features of Connective Tissue Disease but lack adequate clinical or diagnostic features to fit a recognisable clinical syndrome. Characteristics range from the presence of a single clinical or laboratory finding, such as a positive ANA, to the presence of a number of clinical or serological features.

Overlap syndrome is typically applied to patients who have two or more distinctly recognisable rheumatic diseases. Classification remains controversial and one approach is to classify rheumatic diseases using antibodies as disease markers.

Useful resources to demonstrate skin lesions: 

Welcome to Skin Deep - Skin Deep (dftbskindeep.com)

https://www.nottingham.ac.uk/research/groups/cebd/resources/skin-of-colour/index.aspx

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