Difference Between Myotonic Dystrophy Type 1 and Type 2?

If you have been diagnosed with myotonic dystrophy type 2 (DM2), you might be wondering if it will eventually progress into myotonic dystrophy type 1 (DM1). The short answer is no: DM2 will never “turn into” or progress to DM1 ^[1][2].

A common misconception is that the “types” (1 and 2) refer to stages of disease severity, like stages of cancer. In reality, DM1 and DM2 are two completely distinct genetic conditions ^[3][1]. Because their root causes are located on completely different genes, having one does not mean you will eventually develop the other ^[1][2].

Different Genetic Causes

Both conditions are caused by genetic mutations known as repeat expansions, which happen when a small section of DNA is abnormally repeated over and over. However, the exact genes and DNA codes involved are completely different:

Because the root causes are located on completely different genes, they remain permanently separate clinical diagnoses ^[1][2]. The only way to definitively tell them apart is through a genetic test ^[1][4].

Severity and Pace of Progression

Patients often wonder which type is “worse.” Generally, DM2 has a milder clinical course and progresses much more slowly than DM1 ^[5][1].

While DM1 can sometimes present at birth or childhood and progress rapidly, DM2 almost exclusively begins in adulthood ^[6][3]. The progression of DM2 typically happens very gradually over years or even decades ^[5][1]. While it can cause significant disability over time, the long-term outlook for maintaining independence is generally more favorable for DM2 than for DM1 ^[5].

Different Patterns of Muscle Weakness

While both conditions share symptoms like myotonia (difficulty relaxing muscles after contracting them), they typically affect different parts of the body:

• Distal weakness in DM1: People with DM1 usually experience weakness first in their distal muscles, which are the muscles furthest from the center of the body ^[2][7]. This includes the hands, lower legs, feet, and sometimes the muscles of the face and neck ^[2][1].
• Proximal weakness in DM2: In contrast, DM2 is classically known for causing weakness in the proximal muscles, which are the muscles closest to the body’s core ^[2][1]. People with DM2 are more likely to notice weakness in their hips, thighs, and shoulders ^[2][7].

How Management Differs

Because the conditions affect the body differently, your daily management will look different from someone with DM1. For example:

• Physical Therapy: A patient with DM1 might need leg braces for “foot drop” or occupational therapy for hand grip issues. As a DM2 patient, your physical therapy will likely focus more on maintaining hip and shoulder strength to help you get out of chairs or lift objects ^[7][2].
• Pain Management: Severe muscle pain is a very frequent and distinct symptom in DM2 that significantly affects quality of life, meaning pain management strategies will likely be a much bigger focus of your care ^[8].

Multisystem Symptoms

Both DM1 and DM2 are “multisystemic,” meaning they can affect more than just the muscles, including the gastrointestinal tract and endocrine system ^[9][2].

Importantly, cardiac involvement (like heart rhythm issues or arrhythmias) is a serious concern for both types ^[10][1]. Because these heart issues can be silent at first, you should ask your doctor about scheduling a baseline electrocardiogram (EKG) and establishing a routine heart screening schedule ^[10][1]. Your healthcare team will tailor your specific monitoring based on your unique symptoms ^[2][11].