An efficacy analysis of whole-body magnetic resonance imaging in the diagnosis and follow-up of polymyositis and dermatomyositis

Abstract

Objectives: To evaluate the value of whole-body magnetic resonance imaging (WBMRI) in diagnosing muscular and extra muscular lesions in patients with polymyositis (PM) and dermatomyositis (DM).

Methods: A retrospective analysis of WBMRI data from PM/DM patients who met the Bohan and Peter diagnostic criteria was performed. X2 test was used to compare the rate of positive diagnosis of newly diagnosed patients using WBMRI, serum creatine kinase test, and EMG. McNemar test was used to compare the performance of WBMRI and chest CT in detecting interstitial lung disease (ILD).

Results: The study included 129 patients (30 PM cases and 99 DM cases). Of them, 81.4% (105/129) showed a visible inflammatory muscular edema on their WBMRI; 29.5% (38/129) had varying degrees of fatty infiltration (9 cases with clear muscular atrophy). Of the 66 newly diagnosed patients, the positive rates of WBMRI, muscle biopsy, serum creatine kinase test and EMG were 86.4% (57/66), 92.4% (61/66), 71.2% (47/66) and 71.1% (32/45), respectively. There was no significant difference in the positive rates between WBMRI and muscle biopsy (X2 = 1.28, P = 0.258). The WBMRI had a higher positive rate than both serum creatine kinase test (X2 = 4.53, P = 0.033) and EMG (X2 = 3.92, P = 0.047). In addition to muscular changes, WBMRI also detected interstitial lung disease (ILD) in 38 cases (29.5%), osteonecrosis in 15 cases (11.6%), and neoplastic lesions (5 malignant; 7 benign) in 12 cases (9.3%). Of the 61 patients who underwent routine chest CT examinations, the WBMRI and CT revealed ILD in 29 cases and 35 cases respectively. There was no significant difference in the sensitivity between WBMRI and CT (p = 0.146).

Conclusions: WBMRI is a sensitive, non-invasive and efficient imaging method. It comprehensively displays the extent of muscular involvement in PM/DM patients, and it has the ability to diagnose other associated extra muscular diseases, such as ILD and systemic malignancy. WBMRI can also help screen steroid-induced osteonecrosis.

Fig 1. 49-year-old male DM patient.

WBMRI showed significantly increased signal intensity (white arrow) in both shoulders, upper extremities, pelvic muscles and lumbar muscles. The severity of muscle edema in both thighs was significantly lower than that in the above-mentioned sites.

Fig 2. 75-year-old male patient, displaying DM with bilateral lung ILD, bilateral femoral head necrosis.

Follow-up WBMRI showed patchy, reticulonodular and ground glass opacities in bilateral lungs; the most pronounced in the lower right lobe (white arrow). Both femoral heads showed the osteonecrosis area (white arrow) surrounded by curving high signal.

Fig 3. 61-year-old female patient, displaying DM with lung ILD, osteonecrosis in both knees.

WBMRI showed bilateral tibia osteonecrosis (white arrow) and fibrous streaks (white arrow) in the outer lung field, suggesting the presence of ILD.

Fig 4. 43-year-old male patient, displaying DM with nasopharyngeal cancer and cervical lymph nodes metastases, multiple bone metastases and bilateral femoral head necrosis.

Figure 4A showed the avascular necrosis at bilateral femoral head (white arrows); and Figure 4B showed swollen lymph node on the left side of the neck (white arrow); Figure 4C showed patchy abnormal high signals in the thoracic and lumbar spine and pelvis (white arrow). Vertebral biopsy confirmed skeletal metastases.

Fig 5. 35-year-old male DM patient, with lung fungal infection and bilateral osteonecrosis of the knee after steroid therapy.

WBMRI showed multiple spherical lesions in bilateral lungs (white arrow), and the osteonecrosis area (white arrow) surrounded by curvy high signal in the upper left tibia.

Fig 6. 60-year-old woman, displaying DM with thyroid cancer.

WBMRI showed enlargement of the left thyroid, in which there were oval-shaped, abnormally high signals (white arrow) that was diagnosed as thyroid cancer by biopsy.