Case report: response in proteinuria due to AA amyloidosis but not Felty's syndrome in a patient with rheumatoid arthritis treated with TNF-a blockade

carriers can function normally when well but any mild illness can set them back considerably. There may be a history of weakness and clumsiness in childhood, unexplained abdominal/chest pains, tachycardias, and pseudohypertrophy of the calf muscles caused by atrophic muscle fibres being replaced by fat and connective tissue [7, 8]. Genetic testing easily establishes whether a patient is a carrier, but to establish genetically whether she is a manifesting carrier X-inactivation DNA studies are required to look for preferentially skewed inactivation of the normal X chromosome, hence rendering the affected DMD X chromosome the dominant one. DMD patients will often have a raised CK and EMG studies will show low-amplitude polyphasic units similar to those seen in inflammatory myopathies. Muscle biopsy shows characteristic but non-specific changes of dystrophy. Immunocytochemical studies give quantitative analysis of dystrophin. This is usually normal or near normal in carriers but significantly reduced or absent in DMD patients and, often more subtly, in manifesting carriers. Dermatomyositis can also present with very similar symptoms. Proximal muscle weakness and skin rashes are the most common features, but the presentation may also include fatigue, fevers, arthralgias, interstitial lung disease, oesophageal dysmotility, myocarditis and dysrhythmias. Investigation reveals elevated CK during the active phase of the disease and EMG showing polyphasic action potentials with short duration and low amplitude. The muscle biopsy in dermatomyositis shows chronic inflammatory cell infiltration in the perivascular as well as the perifascicular regions. Perifascicular atrophy is diagnostic of dermatomyositis. MRI of the affected muscles depends on the chronicity and activity of the disease. In acute myositis it shows non-homogeneous increased signal intensities, especially on T2-weighted fatsuppressed sequences. Oedema-like changes on T2 sequences are more typical of acute active disease while replacement with fat is characteristic of chronic, inactive myositis [9] (Fig. 1). X-rays will often show subcutaneous calcification, particularly in the juvenile form of dermatomyositis. Our patient had several features of both diseases. The presence of fevers, arthralgias, subcutaneous calcification and perivascular inflammation with perifascicular atrophy on muscle biopsy in the presence of normal dystrophin staining and inconclusive X-inactivation studies lead us to conclude that our patient is a carrier for DMD who developed low-grade dermatomyositis that has responded to low-dose immunosuppression. Informed patient consent was obtained.