Steroid myopathy: evaluation of fiber atrophy with T2 relaxation time--rabbit and human study.
OBJECTIVE
To determine whether muscle fiber atrophy associated with steroid myopathy can be detected with T2 relaxation time.


METHODS
Animal and human studies were approved by the ethics committee. Informed consent was obtained. Twelve rabbits were divided into a group that received 3 mg/kg of triamcinolone subcutaneously each day for 10 consecutive days (n = 6) and a control group that received saline (n = 6). Magnetic resonance (MR) imaging was performed before and after treatment. T2 and fat deposition ratio (FDR) of soleus and gastrocnemius muscles before and after treatment and between control rabbits and rabbits treated with steroids were compared by using two-way repeated analysis of variance and Bonferroni post hoc test to evaluate effects of steroid treatment. After imaging, rabbits were sacrificed. Extracellular space ratio (ECSR) and fiber diameter were examined. Correlation among T2, ECSR, and diameter of type 2 muscle fibers was analyzed with a Pearson correlation test with Bonferroni correction in gastrocnemius to determine factors affecting T2. In humans, T2 relaxation time and FDR of both muscles were compared between volunteers not treated with steroids and patients treated with steroids by using an unpaired t test to evaluate the effects of steroids.


RESULTS
In rabbits, T2 of gastrocnemius muscle was significantly (P < .01) longer after steroid treatment than before steroid treatment and was also significantly (P < .01) longer than after saline administration. T2 of the gastrocnemius showed no significant difference in control rabbits before or after saline administration or in control rabbits and rabbits before steroid administration. T2 of the soleus muscle or FDR of either muscle showed no significant difference. There was a significant correlation (P < .01) among T2, ECSR, and diameter of type 2 muscle fibers in the gastrocnemius. In humans, T2 of the gastrocnemius was significantly (P < .01) longer in patients than in volunteers. T2 of the soleus or FDR of either muscle showed no significant difference.


CONCLUSIONS
Muscle fiber atrophy associated with steroid myopathy is detectable as prolongation of T2 relaxation time in the gastrocnemius muscle; the authors believe prolongation of T2 relaxation time is mainly due to increased ECSR reflecting type 2 muscle fiber atrophy.
Hatakenaka
Masamitsu
M
Department of Clinical Radiology, Graduate School of Medical Sciences, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka City 812-8582, Japan. mhatake@radiol.med.kyushu-u.ac.jp
Soeda
Hiroyasu
H
Okafuji
Takashi
T
Yabuuchi
Hidetake
H
Shiokawa
Satoshi
S
Nishimura
Junji
J
Honda
Hiroshi
H
D000328:Adult; D000818:Animals; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D009133:Muscular Atrophy / Q000139:chemically induced* / Q000473:pathology*; D009135:Muscular Diseases / Q000139:chemically induced / Q000473:pathology; D011817:Rabbits; D013256:Steroids / Q000009:adverse effects*
D013256:Steroids