The patient was a young man lying comfortably in bed
He was of average height and weight
On examination of the lower limbs the trainee noted that there was no major change in the overall size of the limbs and there were no trophic changes in the skin. These findings indicated that the lesion was not long standing.
The muscles of the lower limb were wasted; there were no involuntary movements. This suggested that the lesion affected the lower motor neurone. The absence of involuntary movement, in particular fasiculations, suggested that the anterior horn cell was not affected.
Tone was flaccid reinforcing the idea that this was a lower motor neurone lesion.
Power was decreased throughout the lower limb with the distal muscles being affected to a greater degree. In keeping with a lower motor neurone lesion. The distribution of the weakness was a paraparesis. What we had now demonstrated was a flaccid paraparesis. This narrowed the possibilities down to just a few (ACES for PACES page 452). Of these options, flaccidity narrowed the possibilities down even further leaving us with the possibility of either a radiculopathy or cauda equina lesion.
Reflexes were absent even with reinforcement, further evidence in favour of a lower motor neurone lesion. Eliciting reinforcement allowed us to see that the upper limbs were functioning normally reinforcing our idea that this was a paraparesis.
It was not possible to test coordination in the lower limbs in view of the weakness.
Sensory examination did not reveal a gross deficit; there was equivocal loss of light touch over the feet. This would be a feature against a cauda equina lesion, as the patient would have had anaesthesia in a saddle distribution.
The most likely diagnosis was a polyradiculoneuropathy.
The candidate was asked whether he would like to ask the patient a question regarding the condition to reinforce the diagnosis. The question was whether the patient’s bladder or bowels were affected. Although autonomic features are common in acute inflammatory demyelinating polyradiculoneuropathy (Guillain-Barre syndrome, AIDP) the bladder is not commonly affected whereas it is commonly affected in cauda equina lesions.
The candidate was also asked whether there was any other physical examination he would like to conduct to exclude a cauda equina lesion. The answer was per rectal examination and testing for anal tone, which would be reduced, and the anal reflex, which would be absent in cauda equina lesions.
Diagnosis
Flaccid paraparesis due to a polyradiculoneuropathy possibly acute inflammatory demyelinating (the onset was over a short duration) or Gullain- Barre syndrome
Revision Tips
Neurology is a difficult subject and is often considered daunting by most candidates attempting the PACES examination.
It is helpful to know the causes of the types of deficit that occur in neurological practice as this will enable one to localise the site of the lesion
Study the causes of wasting of muscles (ACES for PACES page 443)
Study the causes of flaccidity (ACES for PACES page 449)
Study the different types of distribution of muscle weakness (ACES for PACES page 451-453)
Study the patterns of sensory loss and their causes (ACES for PACES page 455-456)
