The current clinical diagnosis of myotonic dystrophy: history and physical examination are the important basis for the diagnosis of myotonic dystrophy. In addition to the development of muscle weakness and atrophy symptoms, the history should also include whether the patient’s motor development milestones are delayed, athletic endurance, sports performance, etc. In addition, it is also necessary to ask the family history, the author treated more than one case of children with DMD, whose mother had a brother with similar symptoms, died before the age of 20, but the child’s father did not know, at this time the family history In this case, the family history should be asked with skill, not only to get the real information needed, but also to pay attention to privacy protection, to avoid creating conflicts in the child’s family. The physical examination of myotonic dystrophy patients should be meticulous and comprehensive, with emphasis on typical signs that are diagnostic for specific subtypes. Physical examination of the motor system includes six aspects: muscle volume, muscle strength, muscle tone, ataxia, involuntary movements and gait, which can provide an important basis for the clinical diagnosis of myotonic dystrophy. The examination needs to fully expose the limbs to observe the muscle volume of trunk and limbs, pay attention to the distribution characteristics of muscle atrophy, the presence of hypertrophy of tongue muscle and gastrocnemius muscle, the presence of pterygoid scapula, the presence of scoliosis, paraspinal muscle atrophy, etc. The muscle strength examination should cover the extraocular muscles, orbicularis oculi, orbicularis oris, cervical flexor, cervical extensor, limb strap muscle, proximal and distal muscle groups of the limbs, to touch the muscle hardness, percussion on the muscle belly to observe the presence of “muscle ball”, observation of gait, squatting standing and whether heel and toe walking, also need to pay attention to the presence of joint contracture and joint hyperextension, of course, also need to carry out routine sensory examination and tendon reflexes, pathological signs examination to serve as a basis for differential diagnosis. For some types of myotonic dystrophy with characteristic clinical manifestations, experienced doctors can quickly confirm the diagnosis through physical examination, and some can even reach “second diagnosis”, such as facioscapulohumeral myotonic dystrophy, ankylosing myotonic dystrophy type 1, etc. with characteristic appearance, typical patients can easily make clinical diagnosis. Targeted ancillary tests are also an important basis for clinical diagnosis of myotonic dystrophy. Creatine phosphokinase (CK) is a sensitive and specific indicator reflecting the destruction of skeletal muscle. For example, CK can be elevated to tens of times normal with ALT, AST and LDH in 3-year-old children with no obvious symptoms of muscle weakness, while CK can be only mildly elevated or even normal in patients with severe myasthenia gravis and significant functional impairment. EMG/nerve conduction examination is mainly used for lesion localization and has limited value in differentiating myotonic dystrophy from other muscle lesions; some characteristic electrophysiological changes can support the diagnosis, such as myotonic discharges have diagnostic value for ankylosing myotonic dystrophy, but it should be noted that myotonic discharges are not only seen in DM, but also in certain ion channel diseases, metabolic myopathies and inflammatory myopathies; for patients with myotonic dystrophy, EMG can objectively reflect the distribution of myogenic damage and the severity of lesions in different muscle groups. Needle EMG sees fibrillation potentials, positive sharp waves and other denervated potentials, which are signs of lesion activity. Genetic testing is an important method to diagnose myotonic dystrophy, and with the increasing popularity of high-throughput sequencing technology, many companies have launched genetic testing “packages” for myotonic dystrophy, and some clinicians do direct genetic screening for patients with a preliminary diagnosis of myotonic dystrophy, but in fact different tests are available for different types of mutations, such as A package covering hundreds of myotonic dystrophy mutations is only suitable for detecting point mutations and small fragment insertion and deletion mutations within the exons of the causative gene, but not for detecting mutations that cause DM1 and FSHD. Therefore, the selection of specific protocols for genetic testing needs to be based on clinical and pathological data, and the results should be interpreted with more caution. Differential diagnosis of myotonic dystrophy: The differential diagnosis of myotonic dystrophy includes the differentiation of myotonic dystrophy from other diseases that cause symptoms of muscle weakness and myasthenia gravis and the differentiation between specific types of myotonic dystrophy. Due to space limitations, the former is the focus here. We know that the symptoms of muscle weakness and myasthenia are caused by lesions in one or more links of the motor conduction pathway. Upper motor neuron lesions are mostly characterized by hyperactive tendon reflexes and positive pathological signs, which are not easily confused with myotonic dystrophy, which needs to be differentiated from lower motor neuron, motor nerve, neuromuscular junction lesions and other myopathies. Diseases involving lower motor neurons include spinal muscular atrophy, Kennedy disease, progressive muscular atrophy (subtype of ALS), post-polio syndrome, etc. Peripheral neuropathies that can mainly involve motor function include multifocal motor neuropathy (MMN), chronic inflammatory demyelinating radiculopathy (CIDP), peroneal muscular dystrophy (CMT), etc. Neuromuscular junction diseases include severe Myasthenia gravis, Lambert-Eaton syndrome, etc.; myopathies that need to be differentiated from myotonic dystrophy include metabolic myopathy, endocrine myopathy, chronic inflammatory myopathy, etc. The impact of protein expression on diagnosis: For subtypes of myotonic dystrophy in which the causative gene and related proteins have been identified, protein expression is of great value for diagnosis. In DMD, for example, antibodies to different regions (N, R, C) of Dystrophin encoded by the causative gene have been commercialized, allowing a qualitative leap in the diagnosis and differential diagnosis of DMD. immunohistochemical staining of muscle biopsies from DMD patients shows Dystrophin-C deficiency, whereas BMD patients can have patchy expression under the muscle membrane. Protein blotting of muscle tissue (Western blot) can also show Dystrophin deficiency in patients with DMD. Various proteins expressed in myofibrillar and nuclear membranes such as Dysferlin, Sarcoglycan, and Emerin are currently available for immunohistochemical staining, while some proteins (e.g., calpain 3) can only be detected by Western blot.