Threads and Fine Threads

To the Editor.—  The recent cooperative study "Uses for Immunofluorescence Tests of Skin and Sera"¹ stated that the speckled nuclear immunofluorescence pattern may be associated with mixed connective tissue (MCT) disease, as described by Sharp et al.² However, Dr Burnham, emphasizing strict attention to nuclear immunofluorescence morphological features, has demonstrated that the nuclear speckles found in MCT disease actually correspond to his nuclear immunofluorescence pattern of threads and fine threads.³ These patterns probably represent the ribonuclease-resistant extractable nuclear antigen antibody of Sharp et al.^2,4,5 Dr Burnham has reported the prognostic importance of nuclear immunofluorescence patterns in lupus erythematosus. He described the thready pattern as being the only particulate pattern not in his good prognostic group, with a 33% incidence of renal involvement.⁵ The reported incidence of renal involvement in MCT disease is extremely low.¹ Can Dr Burnham comment on the low degree of renal involvement