DISCUSSION
In that case report, we described a case of IBM induced with long-term
imatinib use. Because IBM is a rarer type of muscle pathology,
identification of IBM and differential diagnosis is important.
Involvement of distal upper and proximal lower extremity, asymmetrical
involvement with both inflammatory and degenerative patterns in EMG,
older age of patient, normal level of CK enzyme, and absence of
malignancy are important clues for IBM (1, 3). Focally increased signal
on fat-saturated gadolinum enhanced T1-weighted images in quadriceps
femoris muscle group sparing of rectus femoris and biopsy including
degenerative changes, mitochondrial abnormality, ragged red fibers and
red vacuoles in addition to inflammation and MHC-1 positivity are
pathognomonic and used in differentiation from other myositis groups
(4). Conventional immunosuppresive agents are ineffective in the
management of IBM and both dysphagia and immobilization are main major
complications leading to subsequent morbidity and mortality (5).
Tyrosine kinase inhibitors have been related to several adverse effects
except for myopathy or myositis (2, 6). To the best of our knowledge,
this is the first case of imatinib induced IBM. In our patient,
improvement of symptoms after cessation of imatinib, confirmed the
trigger of IBM and found out the value of etiology identification to
relieve symptoms in addition to supportive care. This is unclear whether
muscle injury developed due to prolonged use or the directly molecular
property of imatinib. However, considering the much longer use of
imatinib in other indications, especially chronic myeloid leukemia,
duration does not appear to be the only reason. In our opinion, the main
mechanism underlying this unexpected side-effect might be related with
the blockage of tyrosine kinase pathway beyond the intended treatment
period in disease remission which triggers a differrent response rather
than the continous prolonged suppresion of bcr-abl kinase-related
protein phosphorylation in myeloid cells. However, considering the wide
use of imatinib in daily practise with a quite safe profile, it is
important to aware of this rare adverse effect to recognize, monitorize
and manage patients more effectively.