Mutations in the filamin C gene (FLNC) cause a myofibrillar myopathy (MFM), morphologically characterized by focal myofibrillar destruction and abnormal accumulation of several proteins within skeletal muscle fibres. We studied 31 patients from four German families to evaluate the phenotype of filaminopathy. All patients harboured the same p.W2710X mutation in FLNC. Haplotype analysis suggested a founder mutation in these German filaminopathy families. The mean age at onset of clinical symptoms was 44 +/- 6 years (range, 24-57 years). Slowly progressive muscle weakness was mostly pronounced proximally, initially affecting the lower extremities and involving the upper extremities in the course of disease progression, similar to the distribution of weakness seen in limb-girdle muscular dystrophies (LGMD). Patients frequently developed respiratory muscle weakness. About one-third of the patients showed cardiac abnormalities comprising conduction blocks, tachycardia, diastolic dysfunction and left ventricular hypertrophy indicating a cardiac involvement in filaminopathy. Serum creatine kinase levels varied from normal up to 10-fold of the upper limit. Magnetic resonance imaging studies showed a rather homogenous pattern of muscle involvement in the lower extremities differing from that in other types of MFM. Myopathological features included perturbation of myofibrillar alignment, accumulation of granulofilamentous material similar to that seen in primary desminopathies and abnormal intracellular protein deposits typical of MFM. Decreased activities of oxidative enzymes and fibre hypertrophy seem to be early features, whereas dystrophic changes were present in advanced stages of filaminopathy. Rimmed vacuoles were detected in only a few cases. The intracellular aggregates were composed of a variety of proteins including filamin C, desmin, myotilin, Xin, dystrophin and sarcoglycans. Therapy is so far limited to symptomatic treatment. The German filaminopathy cohort, the largest group of patients studied so far, shares phenotypic features with LGMD and presents with characteristic histopathological findings of MFM.
Objective
To compare muscle imaging findings in different subtypes of myofibrillar myopathies (MFM) in order to identify characteristic patterns of muscle alterations that may be helpful to separate these genetic heterogeneous muscular disorders.
Methods
Muscle imaging and clinical findings of 46 patients with MFM were evaluated (19 desminopathy, 12 myotilinopathy, 11 filaminopathy, 1 αB-crystallinopathy, and 3 ZASPopathy). The data were collected retrospectively in 43 patients and prospectively in 3 patients.
Results
In patients with desminopathy, the semitendinosus was at least equally affected as the biceps femoris, and the peroneal muscles were never less involved than the tibialis anterior (sensitivity of these imaging criteria to detect desminopathy in our cohort 100%, specificity 95%). In most of the patients with myotilinopathy, the adductor magnus showed more alterations than the gracilis muscle, and the sartorius was at least equally affected as the semitendinosus (sensitivity 90%, specificity 93%). In filaminopathy, the biceps femoris and semitendinosus were at least equally affected as the sartorius muscle, and the medial gastrocnemius was more affected than the lateral gastrocnemius. The semimembranosus mostly showed more alterations than the adductor magnus (sensitivity 88%, specificity 96%). Early adult onset and cardiac involvement was most often associated with desminopathy. In patients with filaminopathy, muscle weakness typically beginning in the 5th decade of life was mostly pronounced proximally, while late adult onset (>50 years) with distal weakness was more often present in myotilinopathy.
Conclusions
Muscle imaging in combination with clinical data may be helpful for separation of distinct myofibrillar myopathy subtypes and in scheduling of genetic analysis.
Reduction of kilovoltage from 120 to 100 kVp resulted in significant reduction of effective dose at pulmonary CT angiography, without significant loss of objective or subjective image quality.
Multidetector CT with VT with a low-dose protocol had high sensitivity and specificity for depiction of tracheobronchial narrowings and/or anomalies. However, tracheal narrowing due to tracheobronchomalacia was difficult to diagnose at single-phase multidetector CT with VT.
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