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.
Purpose: To distinguish mixed connective tissue disease (MCTD) from progressive systemic sclerosis based on the discriminant function of Ishikawa et al.
Specialty: Immunology/Rheumatology
Objective: differential diagnosis and mimics, red flags
ICD-10: M35.1, M34.0,
