CASE REPORT
An 81 years old male with the history of dilated cardiomyopathy and congestive heart failure and an operated gastrointestinal stromal tumor (GIST) of stomach 8 years ago was admitted due to urinary tract infection. He had progressive loss of weight of approximately 50 pounds and muscle strength in the last 6 months and was completely immobile for the last four months. On physical examination, he was left-handed, grip impairment and diffuse loss of muscle strength on extremities prominently at distal of right upper limb and proximal of lower limbs as 3/5 without any rash, arthritis, and organomegaly were seen. Owing his comorbidities, he was under dabigatran, furosemide, bisoprolol, and 400 mg/day of imatinib for the last 8 years. The patient declared that he gave up routine oncologist follow-up for 5 years and continued to take imatinib only. Laboratory showed hemoglobin 9.9 gr/dl, white blood cells 11800 109cell/L, neutrophils 9900 109cell/L, CRP 167 mg/L, creatinine 1.4 mg/dL, albumin 2.9 gr/dL, and pyuria on urine analysis. Liver enzymes, thyroid function tests, and coagulation parameters were normal. After antibiotherapy, acute phase reactants returned to normal range.
Owing to systemic symptoms and progressive muscle weakness; serologic tests including anti-nuclear antibody (ANA), extractable nuclear antigen (ENA) panel, anti-jo1 antibody, and serum creatine kinase (CK) levels were requested and found in normal range. In bilateral thigh MRI both acute and chronic findngs of muscle damage were observed. Figure 1 a and b shows signal changes consistent with focal myositis were observed in the bilateral quadriceps femoris muscles, especially in vastus medialis muscles with right side dominance, and atrophic fatty degeneration in the distal musculotendinous junction of the semimembranosus muscle most prominently. Both muscle atrophy and asymmetric fatty infiltrations suggesting chronic changes, and hyperintensity on T2-weighted fat-suppressed images suggesting acute myositis with normal levels of CK were consistent with IBM.
Electromyography revealed sural and supperoneal sensory unresponsiveness, prolongation in the distal latency of the median response on the right in sensory, while long distal latency and low amplitude of the median, ulnar and tibial responses, and peroneal unresponsiveness on the right were observed in motor nerve conduction studies. In the needle EMG examination, short-term, polyphasic, low-amplitude motor unit action potentials (MUAPs) and early participation patterns were observed in right deltoid, biceps, first distal interosseus, vastus medialis, and iliopsoas muscles and bilateral tibialis anterior and gastrocnemius muscles. All were interpreted as diffuse myogenic involvement in both neurogenic and myopathic manner.
PET/CT was performed to evaluate any recurrence or metastasis of GIST and exclude paraneoplastic causes and revealed physiological FDG uptake except for chronic inflammation due to remitting epididymoorchitis in the right testis. Urological evaluation, upper gastrointestinal gastroscopy, and colonoscopy were benign with no findings of relapsed GIST.
Biopsy taken from the right quadriceps femoris muscle revealed type 2 atrophy with fatty replacement, diffuse degeneration-regeneration, red-rimmed vacuoles, ragged red fibers indicating mitochondrial abnormality, and focal MHC-I positivity on muscle tissue with inflammatory cell infiltration but not vasculitis and found to be compatible with IBM (Figure 2 a, b, c, and d).
Imatinib was discontinued because there was no indication of use with proven disease remission and no other suspicious reason or malignancy was detected for IBM development. The absence of dysphagia and resistive infection led us to follow-up him without IvIg administration. One month after imatinib cessation, he was able to sit in bed and his weight was stable. In the fourth month, his weight gain was evident, and both general health status and muscle weakness were improved. At his last examination, grip impairment was resolved and MRC grades of both upper and lower limbs were 4-5/5. He became more independent and mobile in bed, started to eat own his own. Since no benefit was expected from immunosuppressive therapy; nutritional support, physical therapy and rehabilitation were given with periodic dysphagia evaluation and concurrent neurology follow-up.