We read with interest the paper published by Boschi et al,¹ in which immunohistochemistry was performed on orbital tissues from patients with thyroid associated ophthalmopathy (TAO) and compared with non-diseased orbital tissue.

Our laboratory recently reported positive TSH receptor staining within normal human muscle fibres, using one of the same antibodies (3G4) as Boschi et al (supplied by Costagliola) and a commercial antibody (3B12).²

Our findings differ from Boschi et al’s as no staining of the muscle fibres was visible in their experience.

Assessing the techniques used suggested some possibilities as to why our findings differ. Our paraffin embedded tissues were subjected to a proteolytic antigen retrieval step, as commonly used in avidin-biotin staining.³ The reason for this is that formalin used in fixation is notorious for altering protein immunoreactivity, and hence masking protein expression.^4,5

Moreover, the amplification immunohistochemistry kit used in our experiments is possibly more sensitive than conventional immunohistochemistry used in the experiments of Boschi et al.⁶

We do not dispute the finding that TSH-R expression is elevated in orbital connective tissue of diseased patients. Combined with our findings, Boschi et al’s paper also suggests that expression of TSH-R on normal muscle fibres is lower than in the connective tissue of diseased patients. Boschi et al have successfully produced more evidence that connective tissues in the orbit are active in TAO affected patients; however, the potential role of the extraocular muscle in the pathogenesis of TAO should also be considered.