Based on my experience, in my view, every patient who visits a clinic desires that a part of the body be examined first. For example, a patient with abdominal pain wishes to have the abdomen examined first. Notably, that organ/area may not be the most important clinically; however, examination of the part can provide a general idea regarding the issue that brought the patient to the clinic and the issue that you, as the clinician, will be required to manage. A meticulous routine physical examination is important.
Examination of the thyroid gland, lungs, heart, skin, and lymph nodes is essential in patients presenting with complaints associated with muscle diseases.
A detailed neurological examination is important for the diagnosis of muscle disease, particularly for neurogenic muscle atrophy. Careful examination can distinguish between motor neuron diseases and peripheral neuropathies. Standard examination methods have been established and are routinely used in clinical practice. These are all well-established and well-accepted methods that are an integral component of a thorough physical examination. Of note, these examination methods need to be applied not only in patients but also in seemingly healthy individuals who may be neurologically asymptomatic. Furthermore, it should be remembered that repeating examination in the same individual can suggest variations in a healthy individual. This information can help to develop a personal database of findings observed in seemingly healthy individuals, and this data can help to evaluate whether findings in a patient are abnormal when compared to this database.
The following muscle parameters must be evaluated：i）volume, ii）strength and, iii）additional features.
Assessment of muscle volume is often difficult in individuals diagnosed with obesity. Careful inspection of the entire body including the back is necessary. Balance of muscle volume can be accurately assessed based on knowledge of the balance in healthy individuals. Information regarding a patient’s background, such as his/her occupation is often useful.
Manual muscle testing (MMT) should be performed based on standard methods. Muscle strength is altered by the length of a muscle or the joint position; therefore, muscle strength should always be evaluated in the same posture. MMT must be modified based on muscle strength. Weak muscles should be examined by loading horizontal movement. Psychological factors can significantly affect MMT. The examiner should pay close attention to any unnatural and unexpected loss of muscle resistance.
Additional symptoms include muscle tone, involuntary movements, and fasciculations.
Pseudohypertrophy may be observed in cases of muscular dystrophy. A few patients with hypothyroidism may present with the mouding phenomenon or myoedema. Muscle pain is common in cases of myositis.
Measurement of proteins that leak from the injured muscle fibers is the most important blood test for investigation of muscle diseases. These tests include measurement of serum levels of creatine phosphokinase (CK), aldolase, alanine aminotransferase, and lactic dehydrogenase. CK is widely used because of its high specificity and sensitivity. Serum CK levels are elevated after exercise; therefore, results of this test on an outpatient basis need careful interpretation. Although it originates from both skeletal and cardiac muscles, examination of isoenzymes is helpful to distinguish its origin. Various serological tests are indicated in cases of collagen vascular diseases, and autoimmune disorders should be considered in the differential diagnosis. Some autoantibodies need to be tested at specialized laboratories; therefore, it is advisable to store some serum samples separately for these specialized tests.
Computed tomography (CT) and magnetic resonance imaging (MRI) are useful to assess the muscle volume and identify inflammatory lesions, respectively in skeletal muscles. Fat-suppressed MRI images are used to distinguish between fat infiltration and inflammatory edema. The examinee should avoid vigorous exercise before the MRI to avoid abnormal high-intensity signals on T2-weighted images obtained following such exercise.
Electrophysiological tests play an important role in diagnosing muscle diseases. Nerve conduction studies are useful to assess peripheral nerve function. When combined with evoked potential studies, these tests are useful for the functional assessment of sensory and motor tracts in the spinal cord and the brain. Repetitive stimulation studies are particularly important for diagnosis of myasthenia gravis and other disorders of the neuromuscular junction. Needle electromyography (nEMG) is an important test to distinguish neurogenic muscle atrophies from myopathies. It can detect abnormal spontaneous discharges such as fibrillation potentials and assess the pattern of discharge called motor unit potentials on voluntary muscle contraction.
The role of genetic studies for diagnostic confirmation of muscle diseases has expanded remarkably in recent years. However, confidentiality and ethical issues need attention with regard to genetic information. Informed consent from the patient or family members is mandatory before such studies.