Serum muscle enzymes and standard inflammatory markers at time of diagnosis in idiopathic inflammatory myopathies – a retrospective analysis

Objectives: To characterise standard inflammatory markers (C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), leucocyte count) and serum muscle enzymes (creatine kinase (CK), myglobine) at the time of diagnosis in patients with idiopathic inflammatory myopathies (polymyositis (PM), dermatomyositis (DM), Jo-1 syndrome (Jo-1), sporadic inclusion body myositis (sIBM)). Methods: We analysed retrospectively levels for CK, myglobine, CRP, ESR, and leucocyte count in patients at time of diagnosis in which muscle biopsy had confirmed the diagnosis of idiopathic inflammatory myopathy. Results: 61 therapy naïve patients with idiopathic inflammatory myopathy were included (PM n=27, DM n=15, Jo-1 n=5, sIBM n=14). Mean age (yrs) was 59.2 in PM, 63.5 in DM, 45.4 in Jo-1, and 65.0 in sIBM. CK (mmol/l x s, normal range<2.41) was highest in Jo-1 (129.4) compared to PM (41.0), DM (35.7), and sIBM (6.6) (ANOVA p<0.01), increases in myoglobin showed a similar pattern. ESR was significantly higher in DM compared to the other groups (ANOVA p<0.05). 7/15 DM patients (47%) had an ESR >35mm within the 1^st hour, 4 of them had a cancer associated DM. ESR ≥35mm was found in 11% of PM (3/27), 0% of Jo-1, and 7% of sIBM (1/14). CRP (mg/l, normal range <0.5) was significantly higher in DM (40.4) and Jo-1 (41.2) compared to PM (9.9) and sIBM (5.4) (ANOVA p<0.001). Normal or mildly increased (<2.0-fold upper limit) CRP levels were found in 93% sIBM and 78% PM, but only 20% Jo-1 (1/5) and 47% DM. Neither ESR nor CRP showed a correlation with serum myoglobine and CK levels. Conclusions: Standard inflammatory markers appear to be useful laboratory markers in the early differenzial diagnosis of myositis and seem to reflect the different ongoing immune activation especially in DM and Jo-1. ESR might help to identify patients with cancer-associated DM or PM/DM in which myositis precedes cancer. However, these marker cannot replace muscle biopsy and autoantibody screening.

Table 1: CRP and ESR at time of diagnosis in idiopathic inflammatory myopathies

	PM	DM	Jo-1	sIBM	ANOVA
CRP (mean)	9.9	40.4	41.2	5.4
(range)	(5.0–69.8)	(5–212)	(7.2–61.5)	(5.0–9.4)	p<0.001
CRP normal (n)	14 (52%)	5 (33%)	0 (0%)	12 (86%)
CRP ≤2.0 fold (n)	23 (85%)	8 (53%)	1 (20%)	14 (100%)
ESR (mm) 1st hour	22.7	39.2	22.5	16.7	p<0.05
(mean, range)	(4–90)	(10–90)	(10–30)	(2–35)
ESR ≥35mm (n)	3 (11%)	7 (47%)	0 (0%)	1 (7%)