Symptoms and Disease Progression

Welander Distal Myopathy (WDM) is a condition defined by its patience. Unlike more aggressive muscle diseases, WDM unfolds slowly over decades, typically making its first appearance in a person’s late 40s or 50s ^[1][2]. Understanding the specific roadmap of this progression can help you prepare for the future while recognizing that you will likely remain mobile and independent for a very long time.

The First Signs: “The Extensor Pattern”

The hallmark of WDM is where the weakness begins. It specifically targets the distal long extensors—the muscles responsible for straightening your fingers and lifting your toes ^[1][3].

• In the Hands: The first sign is often a slight clumsiness in the hands or difficulty extending your index or middle fingers ^[4]. This can make it hard to release your grip, use a keyboard, or perform fine motor tasks like buttoning a shirt or turning a key ^[1].
• In the Feet: You may experience “foot drop,” where the front of your foot drags slightly when you walk ^[5]. This often leads to easy tripping, especially on uneven surfaces or rugs ^[2].

Why It’s Often Misdiagnosed

It is very common for WDM to be mistaken for peripheral neuropathy (nerve damage) during the early stages ^[3]. This is because the distribution of weakness—starting at the hands and feet—looks remarkably similar to nerve issues like Charcot-Marie-Tooth (CMT) disease ^[6].

However, there are two key differences that set WDM apart:

1. Lack of Sensory Loss: Peripheral neuropathy almost always includes numbness, tingling, or “pins and needles” sensations ^[7]. In WDM, the problem is strictly in the muscle; your ability to feel touch, temperature, and pain usually remains completely normal ^[1].
2. The EMG Signal: An Electromyography (EMG) test can tell the difference. While a neuropathy shows a “neurogenic” pattern (nerves not firing properly), WDM shows a “myopathic” pattern, which indicates that the nerves are healthy but the muscle fibers themselves are weak ^[2].

Progression Over the Decades

The progression of WDM is notably slow, often measured in decades rather than years ^[2].

• First Decade (Onset to 10 years): Weakness is usually confined to the fingers and toes. You may need to adapt how you hold tools or pay more attention to your footing while walking ^[1].
• Second and Third Decades: The weakness may slowly involve more of the hands and ankles. Over time, weakness may also develop further in the feet, leading to more pronounced “foot drop” ^[5]. While the gait becomes more disturbed, the hallmark of WDM is the preservation of walking ability ^[8]. Many patients continue to walk independently well into their 70s and 80s ^[2].
• Long-Term: Over many years, a muscle MRI might show fatty replacement in the distal leg muscles, meaning the muscle tissue is slowly being replaced by fat cells ^[2]. While this sounds concerning, it is part of the very slow natural history of the disease and is the reason for the gradual loss of strength.

A Note on Variability

While the “classic” form of WDM is a pure muscle disease, some relatives may have very mild symptoms that they never even report to a doctor, while others may show a slightly different pace of progression ^[4]. This is known as phenotypic variability, and it is one reason why a detailed family history is so helpful for your medical team ^[1].