Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (10 page)

   The disease is almost exclusively found in individuals >50 years of age. Patients typically present with general malaise, fatigue, as well as aches and morning stiffness in the shoulder, hip girdles, neck, lower back, and knees. Loss of appetite, unintentional weight loss, and depression are also common findings.

   PMR develops in nearly 50% of patients with giant cell arteritis (GCA), and 15–30% of patients with PMR eventually develop GCA.

   Laboratory Findings

Laboratory finding are nonspecific.

   ESR is markedly elevated (>40 mm/hour, but values >100 may be seen). However, some patients with mild disease may have only slight elevations of ESR.

   CRP is elevated and considered a more sensitive marker than ESR.

   Serologic tests such as RF, ANA, and anti-CCP antibodies are typically negative.

Suggested Reading

Dasgupta B, Cimmino MA, et al. 2012 provisional classification criteria for polymyalgia rheumatica: a European League Against Rheumatism/American College of Rheumatology collaborative initiative.
Ann Rheum Dis.
2012;71(4):484–492.

POLYMYOSITIS, DERMATOMYOSITIS, AND INCLUSION BODY MYOSITIS

   Definition

   Polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM) are related inflammatory myopathies that share common features, including muscle weakness and inflammatory infiltrates on a muscle biopsy.

   PM and DM are characterized by a subacute onset of symmetric proximal muscle weakness, common involvement of other organ systems such as lung and skin, a strong association with autoantibodies, and responsiveness to immunosuppression. Both are widely accepted as having an autoimmune basis. Cutaneous involvement is the primary clinical feature distinguishing patients with DM from those with PM.

   In contrast to PM and DM, patients with IBM typically have slowly progressive weakness in both proximal and distal muscles, rarely have other extra-muscular involvement or autoantibodies, and most often do not respond to immunosuppressive therapies. A muscle biopsy showing the presence of typical inclusion bodies is diagnostic for IBM.

   Who Should Be Suspected?

   Patients with PM and DM typically present with progressive proximal muscle weakness and evidence of muscle inflammation. They may also have constitutional symptoms and evidence of involvement of other organs (e.g., interstitial pulmonary disease, polyarthritis). DM patients can be differentiated by having specific cutaneous signs such as Gottron papules or heliotrope eruption.