Detection of the membrane attack complex as a diagnostic tool in dermatomyositis.
BACKGROUND
Currently there is no reliable diagnostic marker to distinguish between the subgroups of idiopathic inflammatory myopathies (IIMs), i.e. dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM). Membrane attack complex (MAC) has been shown to be involved in the pathogenesis of dermatomyositis but its role as a diagnostic marker has not been evaluated.


OBJECTIVE
To assess the diagnostic utility of MAC deposition in distinguishing dermatomyositis from other neuromuscular disorders.


METHODS
Immunohistochemical detection of MAC deposition on endomysial microvessels was carried out on 127 muscle biopsies comprising of 21 cases of dermatomyositis, 42 other IIMs and 64 non-IIM neuromuscular diseases.


RESULTS
MAC deposition showed a high sensitivity (80.9%) and specificity (85%) to differentiate DM from other IIMs. Its specificity was higher (98.4%) in discriminating DM from non-IIM muscular diseases and IIM from non-IIMs.


CONCLUSIONS
MAC deposition can serve as a reliable marker to distinguish DM from other IIMs (i.e. PM and IBM) as well as from non-IIM diseases. It can also serve as a useful adjunct in diagnosis of IIMs when there is diagnostic dilemma with their morphologic similarities. These results provide further credence to the long-standing view that MAC-mediated capillary destruction is involved in the immunopathogenesis of DM.
Jain
A
A
Department of Pathology, All India Institute of Medical Sciences, New Delhi, India.
Sharma
M C
MC
Sarkar
C
C
Bhatia
R
R
Singh
S
S
Gulati
S
S
Handa
R
R
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D001706:Biopsy / Q000379:methods; D002648:Child; D002675:Child, Preschool; D015938:Complement Membrane Attack Complex / Q000378:metabolism*; D003882:Dermatomyositis / Q000175:diagnosis* / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D055806:Microvessels / Q000378:metabolism; D008875:Middle Aged; D009132:Muscles / Q000473:pathology; D009220:Myositis / Q000175:diagnosis / Q000378:metabolism; D018979:Myositis, Inclusion Body / Q000175:diagnosis / Q000378:metabolism; D017285:Polymyositis / Q000175:diagnosis / Q000378:metabolism; D015203:Reproducibility of Results; D055815:Young Adult
D015938:Complement Membrane Attack Complex