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We read with interest the recent report by Padua et al 1 on a body building champion with an isolated mononeuropathy of a distal branch of the femoral nerve, having recently seen a similar patient, with a different cause.
A 39 year old sports physiologist underwent a resting muscle biopsy using the Bergstrom technique, for research purposes. He had previously undergone eight of these biopsies on the other leg without adverse effect, and this biopsy was performed by an experienced operator. Under lignocaine anaesthesia the biopsy needle was inserted. As manual suction was applied followed immediately by closing the biopsy needle, the subject had an intense feeling of cramp (that had not been noticed with previous biopsies). The site of the biopsy was 5 cm lateral to the midpoint between the patella and the anterior superior iliac spine. Over subsequent months wasting of the distal lateral vastus lateralis muscle was noted. An EMG 3 months after injury showed increased insertional activity, fibrillation potentials, and positive sharp waves with no activation of motor unit potentials in the distal fibres of the vastus lateralis muscle. A further EMG 6 months after the biopsy showed evidence of reinnervation.
In our patient, the distal mononeuropathy was traumatic, and clearly related to the needle biopsy. A distal motor branch of the femoral nerve as identified in the anatomical studies of Padua et al 1 was traumatised by the biopsy. It does raise the possibility of an alternative mechanism for the patient of Paduaet al which was not considered in the article, and can be difficult to verify by clinical history alone. The use of anabolic steroids is very prevalent among body builders with the lateral thigh being a common site of administration. Direct injection could have traumatised the nerve, and may also explain the lack of any improvement with time. It is also noted in the illustration of the unaffected leg, that a small dimple is present in the skin at a site where the distal motor branch may be vulnerable, although this is significantly more distal than the biopsy site in our patient. This may, however, be an indicator of previous injections to the lateral thigh.
The authors reply:
We are grateful for the response of Silbert et al. In our paper1-1 we described an isolated mononeuropathy of a distal branch of the femoral nerve and hypothesised that stretching and compression of the nerve had probably occurred during strenuous exercise.
We agree with the possibility of a traumatic nerve lesion due to needle injection and we have knowledge of some cases of this kind of nerve injury in body builders, but in the case reported in the article, we specifically asked the patient if drug injections had been carried out in the thigh. He replied that he had never used this kind of drug administration. Moreover, our patient did not refer to any pain in the thigh, whereas in the case of Silbert et al an “intense cramp” was felt by the subject. Concerning the figure, detailed clinical examination of both thighs had been performed and no suspected “dumping” was seen. We think that the effect in the figure could rather be due to the hypertrophy of a nearby muscle and as noted it is distal to the site of the femoral nerve branch.
For these reasons, the hypothesis of needle injury was not considered in the article, but we agree that in the case of nerve lesion in body builders, a needle injury (for anabolic drug injection) must always be suspected.