As muscle diseases share common presentation and selectivity in muscle affection, they may not be detected clinically; so, it is important to combine both clinical and radiological assessment to reach the most probable diagnosis , to guide genetic counseling, cardio respiratory risk evaluation, prognostic assumption, and future therapeutic possibilities .
Ultrasound can detect the same patterns of muscle affection as MRI , it has no known contraindications and can provide real-time information related to muscle activation and movement patterns; so, selective substitution of muscle ultrasound for MRI can result in significant cost-saving for the health care system .
This study aimed to describe the effect of combining both clinical and radiological assessments to limit the differential diagnosis and reach the most probable one in patients with picture suggestive of muscle diseases. Also, we aimed to assess the role of ultrasound as an initial screening tool in evaluation of muscle diseases as an alternative to MRI.
The clinical assessment could reach a main provisional probable diagnosis in certain cases, for instance, in Duchene muscular dystrophy (DMD), since the clinical presentation is rather classic: young boys with delayed motor milestones, calf hypertrophy, and positive Gower’s sign . Limb girdle dystrophy 2B (LGMD2B) (dysferlin) presents with characteristic heal strike and prominent weakness and atrophy of one head of biceps brachii . Myotonic dystrophy (DM) characteristically has positive myotonic phenomenon . FSHMD has facioscapulohumeral weakness with positive Beevor’s sign . Polymyositis presents with sub-acute onset of dyspnea, muscle pains, and bulbar symptoms. Dermatomyositis has additional skin lesions .
The clinical assessment was sometimes not helpful, may be due to the absence of selective muscle affection, as in cases of delayed presentation or early presentation before the appearance of any clinical clues, such as in cardiac or respiratory affection . Ultrasound can detect focal or patchy abnormalities within muscle groups, as in the affection of the part of a muscle that spares the other one, and can be performed quickly and at the patient’s bedside; so, it could be added to the routine evaluation of muscle diseases .
We compared ultrasound results with MRI for 15 patients (40%); the concordance ratio of ultrasound ranged from 78 to 100%, it was 100% in 10 patients (67%). It was performed safely in the case of floppy infants, and the moth-eaten appearance could differentiate spinal muscular atrophy (SMA) from myopathy . We found that ultrasound was as informative as an MRI as it was previously stated .
Ultrasound with or without MRI confirmed the clinical diagnosis in 20 patients and added to the diagnosis for the other 13 patients; so, it helped in the diagnosis of 33 patients (87%). It can detect quadriceps sparing myopathy, selective affection of one head of gastrocnemius as of medial head of gastrocnemius and soleus more than lateral head in FKRP (LGMD2I) and calpain-3 deficiency (LGMD2A), and selective affection of lateral head of gastrocnemius as in LGMD2B (dysferlin) .
In patients with early contractures, the clinical assessment produced a differential diagnosis of LGMD2A, Bethlem myopathy, and EDMD . The ultrasound and MRI can differentiate between them as the selective affection of the medial head of gastrocnemius and soleus more than the lateral head in calpain-3 deficiency (LGMD2A), selective involvement of the soleus in x-linked EDMD , and affection of the periphery of the gastrocnemius and soleus muscle, showing a rim in between them and the special affection of the middle of the rectus femoris muscle, and the central shadow sign in Bethlem myopathy .
In patients with limb girdle pattern of weakness with calf hypertrophy, the ultrasound helped the diagnosis by detecting the affection of the medial head of gastrocnemius and soleus more than the lateral head in FKRP (LGMD2I), greater affection of gastrocnemius than soleus in Becker muscular dystrophy (BMD). So, in the case of preferential affection in calf muscles that cannot be detected clinically, both MRI and ultrasound and even ultrasound alone detected differences between both heads of gastrocnemius and gastrocnemius and soleus .
Also, in myotonic dystrophy, a characteristic perifemoral semilunar pattern of affection was found . In peripheral floppy infant patients, the ultrasound was used safely without the risk involved in anesthesia as in MRI; it helped to narrow down the differential diagnosis, as it differentiated between whether it was caused due to myogenic or neurogenic disease and whether the echogenicity was homogenous as in myogenic diseases or inhomogeneous as in SMA . Based on the selectivity of muscle affection, it differentiated between different types of congenital myopathies and congenital muscular dystrophy (MD), congenital myasthenia, and connective tissue (CT) disease, or CT-related myopathy. In one patient with myopathy with limb girdle pattern of weakness, imaging detected nearly normal muscle signal that pushed us to search for a secondary myopathy, and we found an elevated PTH level. When an adult onset SMA presented with an LGM-like clinical picture, with CK elevation, ultrasound differentiated SMA from myopathy by the presence of moth-eaten appearance; also, it detected the presence of fasciculation. Further, the ultrasound detected the presence of myokymia in patients with limb girdle weakness and calf hypertrophy, directing the diagnosis towards rippling muscle disease. There was a group of undiagnosed patients; in this group, radiological assessment did not add suggestions for diagnosis, which may be due to diffused muscular fatty infiltration or lack of specific patterns of muscular affection .
In our study, we found that the long duration of illness may not be an obstacle in detecting selectivity of affected muscles, as in advanced BMD, less affection of soleus, more than the gastrocnemius was observed, and even after more than 20 years, imaging detected quadriceps sparing myopathy, and more affection of lateral head of gastrocnemius in LGMD2B. However, in some patients, diffused affection and lost selectivity was also observed; also, we found no relation between the ultrasound findings and the age of patients, similar to Zaidman and his colleagues’ (2011) findings . This is in contrast to Trip and colleagues (2009), who found an increase in echo-intensity in the muscles with age, due to age-related replacement of muscle tissue by fat and fibrosis .
We found no relation between the level of CPK and ultrasound findings, as in DMD, CPK may be markedly elevated, but the ultrasound still could detect more affection of the muscles of anterior compartment and adductors, and in FSHMD, when CPK was usually normal, diffused affection of the muscles was observed, and asymmetrical affection formed our indicator.
So, the level of CK will not limit the use of ultrasound. Tieleman and colleagues (2012) found no relation between muscle echo-intensity and CPK level .
It was not necessary to find that weaker muscles had more echo-intensity than other muscles, as an ultrasound may detect more affection in the muscles which could not be detected clinically. In contrast to our results, Jansen and colleagues (2012), in a study on boys with DMD, found that there was a negative correlation between the echo-intensity of the muscles and the muscle strength .
In our study, we found that when FSHMD was suspected clinically, there was no need to do an ultrasound, as most of the patients reported the pain after a long duration, so the selectivity was lost from the asymmetrical affection that was detected clinically; therefore, we will not recommend ultrasound for patients with FSHMD.
Ultrasound can be used for follow-up of patients, especially when MRI cannot be done due to the presence of pacemaker or severe pulmonary problems , also when there is a risk involved with anesthesia as when congenital myopathies are suspected .
Ultrasound can detect changes in the muscle with regard to disease progression or change in the muscles due to treatment; so, it can be used to follow-up on the disease progression and results of treatment .
In conclusion, combination of clinical and radiological assessments of muscle diseases can suggest a main provisional probable diagnosis, especially when genetic diagnosis is not accessible or expensive, or to provide a guide to the proper genetic testing when it is available. Ultrasounds can be used as a routine tool to screen and follow-up on muscle diseases and as alternative to MRI.