Physical Examination: A physician experienced in the treatment of neuromuscular disorders can suspect myotonic dystrophy based on the physical examination and interaction with the patient. In most of the instances, patients report of recurrent pain in the abdomen, constipation and obstetric complications. Affected men have a characteristic facial appearance as revealed by long face and frontal baldness. The pattern of muscle involvement and muscle wasting (muscles in the face, neck, lower arms and legs) can also be used to establish the diagnosis. An eye examination can reveal the presence of a specific type of cataract, most commonly seen in MMD patients. If a physician suspects his patient to have MMD, he may check for signs of myotonia by slightly tapping the affected area with the help of a rubber hammer. Rapid contraction of the muscle followed by delayed relaxation is seen in patients with myotonic dystrophy.

Electromyography: The electrical activity of the muscles and nerves are tested, providing valuable information regarding the diagnosis. Small needles are inserted into the affected muscles and the electrical activity is tested.

Muscle Biopsy: A small piece of the affected muscle is withdrawn using a fine needle and is then analyzed under the microscope by a pathologist. A specific pattern of muscle architecture may help in establishment of the diagnosis.

Genetic Tests: Although the above-mentioned tests can provide an idea about the presence of muscular dystrophy, a definite conclusion about the clinical condition may not be possible without genetic analysis. In this test, blood sample is drawn from the patient, the DNA extracted and tested for the presence of the disease.