Myotonic dystrophy is a large group of diseases caused by different genetic mutations, in which patients mainly present with progressive limb weakness and muscle atrophy, without sensory abnormalities. These diseases have common features: they mostly start insidiously in childhood, adolescence, and youth, and mainly manifest as symmetrical weakness of the limbs, with more pronounced proximal limbs. Patients often have difficulty going upstairs, squatting, and lifting the upper limbs, and later develop distal limb weakness, such as fine motor effects of both hands, and muscle atrophy and limb weakness slowly increase over time, without sensory abnormalities such as numbness and pain in the limbs during the course of the disease. A clear family history exists in some patients. What tests are needed to confirm the diagnosis of myotonic dystrophy when a patient presents with muscle atrophy and limb weakness? Medical history is important, usually the patient presents with abnormal running and poor sports performance since childhood, with slow aggravation of symptoms. Physical examination reveals decreased muscle volume, decreased muscle strength, and decreased or absent tendon reflexes in the limbs. Laboratory tests reveal a significant increase in muscle-related enzymatic indicators such as creatine kinase (CK) in the full blood biochemistry. In the early stages of the disease, patients may have creatine kinase around 4000 -6000 U/L (normal is below 200 U/L), and in some patients it may even rise above 10000 U/L, especially in pediatric patients. Electromyography may show myogenic changes. Muscle NMR can reveal signs such as atrophy of the corresponding muscles and muscle steatosis. When the above tests suggest abnormalities, the presence of progressive myotonic dystrophy is often highly suspected. When is an EMG and muscle biopsy necessary? Generally speaking, whenever there is weakness in a limb, if there is no contraindication, electromyography should be completed to understand whether the weakness is caused by neuropathy or muscle lesion itself, electrophysiological examination plays a role in pinpointing the problem, if the electromyography supports the muscle problem itself, muscle biopsy needs to be further completed to clarify the nature of muscle lesion, whether it is myotonic dystrophy, inflammatory myopathy, or Myopathy-like changes, etc., which cannot be replaced by other tests. In an era when genetic testing is not widely available, muscle biopsy is arguably the only gold standard for the diagnosis of muscle lesions. For the majority of muscle lesions, muscle biopsy can be useful in clarifying the nature of the lesion. What if some minor patients cannot tolerate muscle biopsy or electromyography? Are there other options? Our experience is that children over the age of 7 or 8 can usually tolerate muscle biopsy, provided that they understand and cooperate well. It is true that some children do not cooperate well with these tests, and non-invasive tests such as genetic and muscle MRI can be used to help with the diagnosis. Is it possible to confirm the diagnosis of myotonic dystrophy directly through genetic testing? In some patients with high suspicion of myotonic dystrophy, especially in the same family, the diagnosis can be clarified by simple genetic tests. However, genetic confirmation of myotonic dystrophy must be viewed scientifically, as a test that is influenced by a variety of factors such as laboratory conditions, laboratory personnel handling and laboratory materials, which may yield erroneous results, and this is when muscle biopsy becomes important. In conclusion, in the process of diagnosing myotonic dystrophy, a clear medical history and corresponding physical examination, combined with laboratory tests such as CK, electromyography and muscle nuclear magnetic examination, these clinical data are the main basis and cornerstone of the diagnosis of the disease, combined with the results of muscle biopsy and finally the results of genetic testing on this basis, finally achieving the unity of clinical, pathological and molecular biology.