Clinical rheurnatology, 1990, 9, N ~ 4

523-529

Correlation between tests of muscle involvement and clinical muscle weakness in polymyositis and dermatomyositis K.E. W.W.

TYMMS,

E.M.

BELLER,

J. W E B B ,

L. S C H R I E B E R ,

BUCHANAN

F l o r a n c e and C o p e P r o f e s s o r i a l D e p a r t m e n t o f R h e u m a t o l o g y , S u t t o n R h e u m a t i s m R e s e a r c h L a b o r a t o r y , T h e U n i v e r s i t y o f Sydney, R o y a l N o r t h S h o r e H o s p i t a l , St. L e o n a r d s , N e w S o u t h W a l e s , 2065, A u s t r a l i a . SUMMARY A correlation study was performed on the degree of muscle weakness in 36 patients with dermatomyositis and 69 with polymyositis in relation to muscle biopsy findings, electromyography (EMG) abnormalities, and serum concentrations of creatine kinase (CK), aspartate aminotransferase (AST) and alanine aminotransferase (AL T) enzymes. Statistically significant correlations were found between muscle weakness and EMG results in patients with polymyositis, and between muscle weakness and serum CK and A S T levels" in dermatomyositis. As expected, correlations were found between the results of the three enzyme determinations in both groups of patients. Key words : Dermatomyositis, Polymyositis, Muscle Biopsy, EMG, CK, AST, ALT, Diagnostic Tests, Muscle Disease. INTRODUCTION

M A T E R I A L S AND M E T H O D S

Although much has been written on the various diagnostic tests for muscle involvement in polymyositis and dermatomyositis (113) it is surprising how little has been published on comparison of the different tests (1,5,7,12). Here we describe a study of 105 patients with polymyositis and dermatomyositis in which we have compared the findings on muscle biopsy, E M G abnormalities and serum enzyme levels. In addition, these tests have been correlated with the degree of muscle weakness.

One hundred and five previously documented patients with either dermatomyositis (36 patients) or polymyositis (69 patients) formed the basis of the study (14). The diagnosis and degree of severity was based on the criteria described by Bohan and Peter (2). Muscle strength was graded according to the Medical Research Council score (15), that is, 5.0 = normal strength, down to 0.0 = no contraction visible. CK levels (normal e 150 IU/ml) were graded on a five point scale: 5 ,~ 2000 IU/ml, 4 = 1000-1999 IU/ml, 3 = 500-999 IU/ml, 2 = 151-499 IU/ml and 1 is 150 IU/ml. The serum aminotransferases, AST and A L T were scored: 5 > = 200 IU/1.4 = 150-199 IU/1.3 = 100-149 IU/1.2 = 41-99 IU/1, and 1, normal, e 40 IU/1. The muscle biopsy changes were scored : Grade 0 = no changes, grade 1 = some mild features of muscle fibre destruction and/or regeneration including necrosis, phagocytosis, increased internal nuclei and basophilia, but no

Received: 28 September 1988 Revision-accepted: 30 May 1990 Correspondence to: E.M. BELLER, Florance and Cope Professorial Department of Rheumatology, Sutton Rheumatism Research Laboratory, The University of Sydney, Royal North Shore Hospital, St. Leonards, New South Wales, 2065, Australia.

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i n f l a m m a t o r y cell infiltrate, g r a d e 2 = s a m e c h a n g e s as in 1, b u t with i n f l a m m a t o r y cell infiltrate, a n d g r a d e 3 = all the a b o v e f e a t u r e s p r e s e n t . T h e E M G was likewise s c o r e d on a 0-3 scale w h e r e : 0 -- n o r m a l , 1 = d e f i n i t e m y o p a t h i c c h a n g e s i n c l u d i n g m u l t i p l e small amplitude short duration polyphasic motor unit p o t e n t i a l s , 2 = s a m e as 1, b u t in a d d i tion, f i b r i l l a t i o n p o t e n t i a l s , a n d 3 = s a m e as 1 a n d 2, b u t in a d d i t i o n , s p o n t a n e o u s high f r e q u e n c y d i s c h a r g e s (14). In this study, for t h e s t a t e d a n a t o m i c a l site o f t h e m u s c l e biopsy, t h e c o r r e s p o n d i n g E M G r e a d i n g a n d clinical m u s c l e s t r e n g t h g r a d e for the s a m e m u s c l e g r o u p was r e c o r d ed. T h e s e 3 v a r i a b l e s w e r e r e g i s t e r e d by 3 diff e r e n t o b s e r v e r s . O n l y a m i n i m a l history was a v a i l a b l e to t h e E M G a n d m u s c l e b i o p s y observers. T h e m u s c l e b i o p s y site was u n k n o w n in 3 cases a n d d i f f e r e n t in r e s p e c t to t h e E M G m u s c l e site in 4 cases. A s t h e l a t t e r biopsy sites w e r e all d e l t o i d muscle, t h e 'equiv a l e n t ' b i c e p s o r t r i c e p t E M G r e a d i n g was used. T h e s e t h r e e m u s c l e s w e r e t h e p r e f e r r e d b i o p s y sites with t h e e x c e p t i o n o f 17 p a t i e n t s w h e r e t h e q u a d r i c e p s o r vastus m u s c l e s w e r e used. T h e m u s c l e v a r i a b l e s in this study (strength, CK, A S T , A L T , b i o p s y a n d E M G ) w e r e m e a s u r e d within o n e m o n t h in all indiVidual p a t i e n t s e x c e p t in 9 cases. O n l y o n e p a t i e n t was s t a r t e d on high d o s e p r e d n i s o l o n e p r i o r to E M G / m u s c l e biopsy, with 15 b e i n g on a small d o s e o f p r e d n i s o l o n e (less t h a n 1 w e e k o r 10 mg). Statistical analysis i n c l u d e d S p e a r m a n ' s rank correlation on the scores of the different tests, a n d e x a m i n a t i o n o f t h e c o n c o r d a n c e o f tests classified only on t h e basis o f n o r m a l a n d a b n o r m a l r a t h e r t h a n by scores, using 2 x 2 tables. RESULTS T h e results w e r e a n a l y s e d s e p a r a t e l y for p a t i e n t s with d e r m a t o m y o s i t i s a n d p o l y m y o sitis in t e r m s o f m u s c l e b i o p s y a n d E M G results. A s c a n b e s e e n f r o m T a b l e s I a n d II, s o m e c o n c o r d a n c e d o e s exist b e t w e e n t h e s e

Table I : Muscle biopsy and E M G scores in patients" with dermatomyositis. (Number of patients in each category) EMG Score 0

Muscle biopsy score 0 1 2 3 4 2 1 0

1

2

4

5

1

2 3 Total

0

2 2 10

3 9

2 3

Total 7 12 7 2 28

(8 cases had incomplete data) Table II : Muscle biopsy and E M G scores in patients with polymyositis. (Number of patients in each category)

EMG Score 0

Muscle biopsy score 0 1 2 3 3 3 5 -

1

7

5

11

2

2 3 Total

3 13

5 1 14

2 18

2 1 5

Total 11 25 12 2 50

(19 cases had incomplete data) Table III : Muscle biopsy and E M G scores in all patients. (Number of patients in each category)

EMG Score 0 1 2 3 Total

Muscle biopsy score 0 1 2 3 7 5 6 9 9 16 3 3 7 5 4 3 1 19 24 27 8

Total 18 37 19 4 78

(27 cases had incomplete data) two test scores in b o t h o f t h e d i a g n o s t i c categories, a n d w h e n b o t h d i s e a s e categories w e r e c o n s i d e r e d t o g e t h e r ( T a b l e III). T h e c o r r e l a t i o n s b e t w e e n m u s c l e weakness a n d t h e d i f f e r e n t tests in p a t i e n t s with d e r m a tomyositis a n d polymyositis are s u m m a r i s e d in T a b l e IV. In p a t i e n t s with d e r m a t o m y o s i t i s t h e only significant c o r r e l a t i o n s w e r e bet w e e n m u s c l e w e a k n e s s a n d C K a n d muscle w e a k n e s s a n d A S T . ( r = 0 . 4 0 a n d 0.38, p = 0.04 a n d 0.03 respectively). T h e muscle e n z y m e s w e r e also significantly c o r r e l a t e d with e a c h o t h e r . ( C K a n d A S T r = 0 . 6 7 , p < 0 . 0 0 1 , C K a n d A L T r = 0 . 5 1 , p =

Correlation between tests of muscle involvement and clinical muscle weakness in polymyositis and dermatomyositis.

A correlation study was performed on the degree of muscle weakness in 36 patients with dermatomyositis and 69 with polymyositis in relation to muscle ...
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