40-year-old woman • fever • rash • arthralgia • Dx?

THE CASE

A 40-year-old woman with no significant medical history sought care at the emergency department for a fever, rash, and arthralgia. On admission, she had worsening bilateral ankle pain and was having difficulty walking. During the previous 3 months, she’d had 3 episodes of tonsillitis, all of which were presumed to be caused by Streptococcus, although no swabs were obtained. Her primary care physician treated her with antibiotics each time: 1 round of amoxicillin 500 mg twice daily for 10 days and 2 rounds of amoxicillin/clavulanate 875 mg twice daily for 7 to 10 days. During the previous month, she’d experienced intermittent fevers ranging from 100.2 °F to 100.8 °F, with no distinct pattern.

The patient said that 2 weeks prior to her admission to the hospital, she’d developed a rash on her right arm, which was papular, nondraining, nonpruritic, and not painful (FIGURE 1). Six days later, the rash spread to her left arm, chest, and back, with a few lesions on her legs (FIGURE 2). A few days later, she developed arthralgias in her hips, knees, and ankles. These were associated with the appearance of large, flat, erythematous lesions on her anterior lower extremities (FIGURE 2). About 5 days before she was admitted to our hospital, the patient was seen at another hospital and treated for possible cellulitis with cephalexin (500 mg 4 times daily for 5-7 days), but her symptoms persisted.

At this point, she sought care at our hospital for her worsening lower extremity arthralgia, difficulty walking, and the persistent rash. An initial lab report showed a white blood cell (WBC) count of 12.6 × 10³/µL (normal range, 4.0-10.0 × 10³/µL) with an absolute neutrophil count of 9.7 × 10³/µL ­(normal, 1.7-7.0 × 10³/µL). Her C-reactive protein (CRP) level was elevated (194.7 mg/L; normal, 0.0-5.0 mg/L), as was her erythrocyte sedimentation rate (ESR) (102.0 mm/h; normal, 0.0-20.0 mm/h). A rapid pharyngeal strep test was negative. Her anti-­streptolysin O (ASO) titer was elevated (2092.0 IU/mL; normal, < 250.0 IU/mL), and her rheumatic factor was mildly elevated (19.0 IU/mL; normal, 0.0-14.0 IU/mL). An antinuclear antibody panel was positive at 1:80. Further testing was performed, and the patient was found to be negative for Sjögren syndrome A, Sjögren syndrome B, anti-Smith, scleroderma-70, double-stranded DNA, and chromatin AB—making an autoimmune disease unlikely.

THE DIAGNOSIS

The patient met the American Heart Association’s revised Jones criteria for the diagnosis of rheumatic fever: She had a positive ASO titer; polyarthritis and subcutaneous nodules (2 major criteria); and ESR > 60 mm/h and CRP > 3 mg/L (1 minor criterion).¹ She started taking naproxen 500 mg twice per day and was given a penicillin G 1.5-million-unit injection. A transthoracic echocardiogram also was performed during her admission to rule out endocarditis; no abnormalities were found.

A few days after starting treatment for rheumatic fever, the patient’s WBC count returned to within normal limits and her joint swelling and pain improved; however, her rash did not go away, leading us to wonder if there was a second disease at work. Dermatology was consulted, and a punch biopsy was obtained. The results showed acute febrile neutrophilic dermatosis, or Sweet syndrome.

DISCUSSION

Sweet syndrome is considered rare, and incidence numbers are elusive.² It has a worldwide distribution and no racial bias.³ Sweet syndrome usually occurs in women ages 30 to 50 years, although it may also occur in younger adults and children.³ The differential diagnosis for Sweet syndrome is broad and includes infectious and inflammatory disorders, neoplastic conditions, reactive erythemas, vasculitis, other cutaneous conditions, and other systemic diseases.³

Three subtypes have been defined based on etiology: (1) classical (or idiopathic) Sweet syndrome; (2) malignancy-associated Sweet syndrome, which is most often related to acute myelogenous leukemia; and (3) drug-induced Sweet syndrome, which is usually associated with granulocyte colony–­stimulating factor treatment.⁴ Our patient had the most common subtype: classical Sweet syndrome.

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