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.