Chronic, Inactive PM/DM

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Increased Expression of Interleukin 1a and MHC Class I in Muscle Tissue

of Patients with Chronic, Inactive Polymyositis and Dermatomyositis

PERNILLA NYBERG, ANNA-LIS WIKMAN, INGER NENNESMO,

and INGRID LUNDBERG

ABSTRACT.

Objective. To investigate if there is a molecular correlate in muscle

tissue to the persisting decreased muscle function in patients with

chronic, inactive polymyositis (PM) and dermatomyositis (DM).

Methods. Muscle function was assessed using a muscle function index of

myositis. To assess disease activity both histopathological

investigation of muscle biopsies and magnetic resonance imaging (MRI)

scans of the thigh muscles were performed. Inactive chronic disease was

defined as persisting muscle weakness and absence of inflammatory

infiltrates in muscle biopsy and absence of signs of inflammation on

MRI. Expression of interleukin 1a (IL-1a), IL-1b, adhesion molecules,

and MHC class I molecules in muscle tissue was investigated with

immunohistochemistry.

Results. Muscle weakness was confirmed by a reduction of muscle function

score.

No signs of inflammation typical for myositis were observed. The most

striking finding in our study was the strong expression of IL-1a and MHC

class I molecules in muscle tissue from patients with inactive chronic

PM and DM. Increased IL-1a expression was evident in capillaries and

increased MHC class I expression was detected in muscle fiber membranes.

Conclusion. IL-1a and MHC class I molecules may have an importance in

the pathogenesis of the chronic muscle weakness and fatigue in patients

with PM and DM. (J Rheumatol 2000;27:940–8)