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Snapshot diagnosis - what is causing this unilateral muscle loss?

Dr Mike Wyndham describes a case where a young rugby player’s worries about muscle weakness led to a genetic diagnosis

Dr Mike Wyndham describes a case where a young rugby player's worries about muscle weakness led to a genetic diagnosis

The patient

This 13-year-old lad presented complaining of weakness affecting his left arm. He was a rugby player and found it increasingly hard to make tackles. He thought that his muscles weren't as large on the affected side.

First instinct

The patient was certainly correct. The muscle bulk was definitely less on the left side and the scapulae were not symmetrical. The likelihood was that it was some type of muscle wasting disorder.

Differential diagnosis

• Muscular dystrophy

• Dermatomyositis

• Polymyositis

Getting on the right track

Polymyositis usually occurs in the 30- to 60-year-old age group, although those in the mid-teenage years may be affected on occasion. In dermatomyositis, there may be rash and early on the muscles may be painful. Both of these symptoms were absent.

The hidden clue

Weakness around the shoulder girdle was the predominant symptom, with visible winging of the scapula. This is a symptom in 80% of people with facioscapulohumeral dystrophy.


Referral to the local genetics unit confirmed the diagnosis of this type of muscular dystrophy.

It is usually transmitted as an autosomal dominant condition but in this case there was no family history. Complications include retinal vasculopathy, which may result in retinal detachment, and atrial arrhythmias.

Dr Mike Wyndham is a GP in Edgware, north London

Unilateral muscle loss Unilateral muscle loss

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