[Lack of therapeutic response: Is it really a rheumatoid Arthritis?]

A 78-year-old female patient was referred to our hospital with treatment-resistant seronegative anti-citrullinated protein antibodies (ACPA)-negative rheumatoid arthritis. The course was characterized by high inflammatory activity and rapid progression of the erosive changes. Under the required high-dose prednisolone therapy, osteoporosis and a deep venous thrombosis (DVT) with pulmonary embolism developed.

A physical examination revealed symmetrical, painful, synovial swelling of the metacarpophalangeal, proximal-interphalangeal and distal-interphalangeal (MCP, PIP, and DIP) joints, finger joint-related violaceous erythema, contractures of the long fingers, and advanced deformities bilaterally. Pain and weakness in the muscles of her proximal extremities led to difficulties in raising her arms and climbing stairs.

The results of laboratory tests showed negative RF (rheumatoid factor) and ACPAs, positive ANA (anti-nuclear antibodies) with titer 1:5120, a nuclear fluorescence pattern and a positive anti-Mi-2 Antibodies in the myositis blot. Conventional x-ray showed erosive and advanced mutilating joint changes in both hands. A magnetic resonance imaging (MRI) of the proximal extremities showed a pronounced muscle atrophy without sights of active myositis.This clinical constellation leads to the diagnosis of an amyopathic dermatomyositis.

The patient was started on intravenous prednisone 100 mg daily, 4 days, followed by rapid dose tapering in the setting of accompanying risk factors such as Osteoporosis, arterial Hypertension and blurred vision. This treatment leads to improvement of symptoms. The basic therapy was switched to Rituximab. An extended tumor search was recommended on an outpatient basis.

A seronegative, ACPA negative, therapy-resistant RA with a rapidly progressive erosive course requires a diagnostic re-evaluation. An erosive, rapidly progressing polyarthritis is commonly seen as manifestation of the subtype inflammatory myopathies associated with anti-Jo 1 antibodies, known as anti-synthetase syndrome. However, associations with the presence of other myositis specific antibodies (MSA) have been also described. The anti-Mi-2 Antibodies are highly specific for dermatomyositis (DM).Amyopathic DM is not common, but the disease course and prognosis do not differ significantly from myopathic DM.As a sudden presentation of DM may be of paraneoplastic origin a further examination in order to exclude malignancy are indicated.