Case study - A schoolgirl with muscle weakness

A detailed history will often provide a likely diagnosis, writes Dr Simon Gowda.

Arm movement was restricted
Arm movement was restricted

As a medical student, I remember hearing a lecture from a venerable professor, who said that 80-90 per cent of the time diagnosis can be deduced from the history and examination alone.

I think that is true in this case.

A 12-year-old girl attended surgery with her mother. Two weeks previously, she had been on a school camping expedition for a weekend. She had noticed a problem with her left shoulder, which started on the Saturday night but got worse on the Sunday. She attended A&E on the Sunday night after returning home.

In A&E, they were unable to explain her problem but advised using an anti-inflammatory medication. The girl was otherwise fit and well.

She was left-handed and had noticed she could not move her arm properly. There had been no fall or accident during the trip. Her symptoms had slightly improved during the two weeks.

Muscle wasting
The camping expedition had involved carrying an 11kg rucksack and walking for most of each day across country. At the end of the trip, she noticed some sensory disturbance in her fingers, which settled, and initially weakness to flexion of her left hand, which had recovered.

The girl was of a thin build. On examination, she had some wasting of the muscles around the scapula on the left side. She could internally and externally rotate both arms. Movements of the elbow and wrist were normal. There was no sensory deficit and no pain whatsoever.

What she could not do was abduct her arm; she could not hold it extended unsupported. In order to try to attempt abduction she would swing her upper body, in order to generate momentum for her arm to abduct.

My thoughts were of a nerve injury, perhaps a neuropraxia. With a muscular problem, I might have expected some pain. The trick movements she attempted reminded me of previous patients I had seen with nerve injuries. Plus, a nerve injury would be consistent with the muscle wasting.

Traction injury
My attention then turned to exactly how this could have happened.

Closer questioning revealed that the straps on the left-hand side of the rucksack had become loose and pulled her left shoulder behind her and down, with the weight pulling on the extended arm. This had been the case for almost the entire hike (12 hours). In essence, what had been set up was a traction-countertraction force centred on the axilla and neck area, which produced a stretching force.

My hypothesis was a neuropraxic brachial plexus injury caused by the traction-countertraction forces. I referred her to an orthopaedic surgeon.

He confirmed the findings and weakness of the rotator cuff muscles and confirmed a neuropraxia or low-violence traction injury to the C5 trunk of the brachial plexus. As she was making a spontaneous recovery, no further action was required and she was scheduled for review after four weeks.

Nerve injuries
A neuropraxia is a transient episode of motor paralysis with little or no sensory or autonomic dysfunction. Neuropraxia describes nerve damage with no disruption of the nerve or its sheath. There is a temporary loss of function, reversible within hours to months. The average is six to eight weeks.

  • Dr Gowda is a salaried GP in Sandbach, Cheshire
Learning points
  • Patients often present days, weeks or months after an accident or event.
  • Ask exactly what happened and the mechanism of injury.
  • It may even be helpful to ask the patient to act out how they moved or fell.

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