Description

Ishikawa et al developed a discriminant function that can help distinguish mixed connective tissue disease (MCTD) from progressive systemic sclerosis (PSS). The authors are from Gunma University in Japan.


 

Parameters:

(1) myalgia

(2) myositis on muscle biopsy

(3) muscle weakness in upper extremities

(4) dry eye

(5) skin sclerosis over lower extremities

(6) shortening of the finger tips

(7) deformities of nail or dropped nail

(8) endured arthritis

(9) elevated serum LDH

(10) LE cells

(11) high titers of antibody to nRNP

Parameter

Finding

Points

myalgia

absent

0

 

present

0.511

myositis on muscle biopsy

absent

0

 

present

1.441

muscle weakness in upper extremities

absent

0

 

present

0.744

dry eye

absent

0

 

present

0.291

skin sclerosis over lower extremities

absent

0

 

present

-0.293

shortening of the finger tips

absent

0

 

present

-0.323

nail deformities and/or loss

absent

0

 

present

-0.387

arthritis

absent

0

 

present

0.391

elevated serum LDH

absent

0

 

mild to moderate

0.782

 

marked

1.564

LE cells

absent

0

 

present

1.616

high titer of anti-nRNP

absent

0

 

present

2.574

 

where:

• I am not sure if "endured" arthritis has a special meaning..

• The cutoff for a marked elevation in the serum LDH needs to be standardized.

 

discriminant score =

= SUM(points for all 11 parameters) - 2.345

 

Discriminant Score

Interpretation

< 0

PSS

0

indeterminate

> 0

MCTD

 

Limitation:

• The LE cell is rarely performed today. An alternative test should be substituted and the function recalculated.

 


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