Sunday, 11 November 2012

The photomicrograph is of a urine specimen from a 15-year-old girl.

The photomicrograph is of a urine specimen from a 15-year-old girl. She has had intermittent fever, malaise, and weight loss over the previous several months. Recently she has developed swollen hands, wrists, and ankles, the pain of which seems out of proportion to the clinical findings. She also complains of cold extremities with some ulcerations of her distal digits. The laboratory test most likely to assist in the diagnosis of this condition is

a. Antibodies to nDNA and Sm nuclear antigens
b. Throat culture for group A ß-hemolytic streptococcus
c. Simultaneously acquired urine and serum bicarbonate levels
d. A urine culture
e. Erythrocyte sedimentation rate

The answer is a. The figure accompanying the question depicts a red blood cell cast characteristically found in the urine of patients with glomerular disease. The fever, malaise, and weight loss as well as the arthritis involving mainly small joints are common findings of systemic lupus erythematosus (SLE). Raynaud phenomenon resulting in digital ulceration and gangrene in a few patients may also be seen. Not described in this patient is the oft-seen malar rash in a butterfly distribution across the bridge of the nose and the cheeks. Simultaneous urine and serum electrolytes for bicarbonate determination hint at renal tubular acidosis that often presents with failure to thrive and unexplained acidosis, sometimes with repeated episodes of dehydration and anorexia. Poststreptococcal glomerulonephritis can present with red cell casts, but the symptoms usually develop 8 to 14 days after the acute throat infection. Urinary tract infections, especially of the upper system, can result in casts, but they would be expected to consist of white rather than red cells. Elevation of the erythrocyte sedimentation rate may be found in SLE, but this is a nonspecific finding noted in many other chronic and acute inflammatory conditions; its diagnostic usefulness in this situation is limited.


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