A 55-year-old man comes to the office for evaluation of chronic muscle weakness. Over the past several months, he has had increasing difficulty walking up stairs and lately has had trouble removing objects out of the overhead cabinets in his kitchen. Temperature is 36.7 C (98 F), blood pressure is 125/80 mm Hg, and pulse is 78/min. On examination, the patient has symmetric proximal muscle weakness and mild muscle tenderness. There is no rash. Muscle biopsy reveals an endomysial mononuclear infiltrate and patchy muscle fiber necrosis. An autoantibody directed against which of the following antigens is most likely to be seen in this patient?

Question

A 55-year-old man comes to the office for evaluation of chronic muscle weakness.  Over the past several months, he has had increasing difficulty walking up stairs and lately has had trouble removing objects out of the overhead cabinets in his kitchen.  Temperature is 36.7 C (98 F), blood pressure is 125/80 mm Hg, and pulse is 78/min.  On examination, the patient has symmetric proximal muscle weakness and mild muscle tenderness.  There is no rash.  Muscle biopsy reveals an endomysial mononuclear infiltrate and patchy muscle fiber necrosis.  An autoantibody directed against which of the following antigens is most likely to be seen in this patient?

Quizplus · Accepted Answer

11ec160b_3b68_d4ee_9249_a742d7076d2c_MD0001_00 Polymyositis is an inflammatory myopathy that typically presents in middle age with an insidious onset of symmetric proximal muscle weakness affecting the upper and lower extremities without significant pain. Dermatomyositis is a similar disorder associated with characteristic skin findings. Both polymyositis and dermatomyositis may occur independently or as a paraneoplastic manifestation of an underlying malignancy (especially adenocarcinoma). Muscle enzyme (eg, creatine kinase, aldolase) levels in inflammatory myopathies are invariably elevated. Autoantibodies, especially antinuclear antibodies, are also present in most cases; anti-histidyl-tRNA synthetase (anti-Jo-1) antibodies are less sensitive but more specific for dermatomyositis and polymyositis. A biopsy can differentiate polymyositis from dermatomyositis, which typically shows an endomysial inflammation without prominent vascular involvement in a scattered or patchy distribution (in contrast, dermatomyositis causes perifascicular inflammation in a segmental pattern without vasculopathy). (Choices A and E) Acetylcholine receptor-binding antibodies occur in myasthenia gravis, which is characterized by episodic weakness that initially affects the ocular/bulbar musculature and worsens with repetition. Antibodies to voltage-gated calcium channels cause Lambert-Eaton myasthenic syndrome (proximal muscle weakness that improves with isometric contraction), which is often associated with small cell lung cancer. Muscle biopsy in these conditions is normal. (Choice B) Anticardiolipin antibodies are typically seen in antiphospholipid antibody syndrome, which is characterized by recurrent vascular thrombosis and/or pregnancy loss. This syndrome is associated with systemic lupus erythematosus, although it may occur independently. (Choice C) Autoantibodies to desmoglein 1 and 3 are seen in patients with pemphigus vulgaris, which is characterized by skin blistering and desquamation. (Choices D and G) Antimitochondrial antibodies are seen in patients with primary biliary cholangitis, which presents with cholestatic symptoms (eg, pruritus, jaundice, steatorrhea) and abnormal hepatic enzyme levels. Anti-smooth muscle antibodies are seen in autoimmune hepatitis, which most commonly presents as chronic progressive hepatitis in middle-aged women. Educational objective: Polymyositis and dermatomyositis are characterized by symmetric proximal muscle weakness and are associated with antinuclear and anti-tRNA synthetase (anti-Jo-1) autoantibodies. Biopsy in polymyositis shows patchy endomysial inflammatory infiltrate (ie, direct invasion of individual muscle fibers), whereas dermatomyositis causes perifascicular inflammation (ie, localized around blood vessels and the septa between muscle fascicles). __________ References: An overview of polymyositis and dermatomyositis. (http://www.ncbi.nlm.nih.gov/pubmed/25641317)

A 55-Year-Old Man Comes to the Office for Evaluation of Chronic