"That ever this should be!" The cellulitis that would not go away

The next patient waiting to be seen at your office today is a previously healthy 2-year-old girl who, according to her father when he called for an appointment, developed a "pimple-like" swelling on the lateral aspect of her right middle finger three days ago. Now, he tells you that he expressed "green fluid" from the lesion, and that erythema developed around it over the following two days. You examine the lesion, offer a diagnosis of cellulitis, and promptly begin treatment with amoxicillin-clavulanic acid.

"Full many shapes ... in crimson colours came"

Within one week of that office visit, however, the family notes progression of the process: Red streaks extend to the base of the middle finger, where a firm nodule develops. Despite multiple antibiotic changes that you institute-cephalexin, ceftriaxone, cefadroxil-the girl's condition does not improve over the ensuing four weeks.

"I fear thy skinny hand!"

At admission for biopsy, the parents confirm the absence of fever throughout the girl's illness. She has been acting well, they report, and has not had other skin lesions on the affected finger, including vesicles or puncture wounds by a thorn, or any musculoskeletal problems. The medical history includes infrequent episodes of otitis media and well-controlled atopic dermatitis. She does not take medications other than the antibiotics you recently prescribed. Immunizations are current. She is not allergic to medications.

The family reports that they have a pet cat but deny that the girl has been bitten or scratched by the animal. The family, including your patient, has not traveled outside the northeastern region of the United States or visited a farm in recent months. The girl has no known exposure to plants or moss, or to a person with tuberculosis. The family history is negative for chronic infection, immunodeficiency, and recurrent skin infection. One parent and one sibling have atopic dermatitis and food allergy. The patient is developmentally normal.

When you examine the girl, who is sitting on her mother's lap, she is somewhat apprehensive but does not appear to be in acute distress. She easily engages in conversation and play, and uses her right hand with little evidence of discomfort. You record vital signs: temperature, 36.2°C; heart rate, 112/min; respirations, 22/min; and blood pressure, 85/55 mm Hg. She is at the 25th percentile for height and weight for her age.

The physical exam is unremarkable except for the known findings on the right hand. The middle finger of that hand is swollen and erythematous but nontender. There is also as a pea-sized nodule in mid-dorsum on the right hand.

"Now wherefore stopp'st thou me?"

You consider the diagnostic possibilities-infectious and noninfectious. An osteoid osteoma of the finger, you recall, may not be painful and is not associated with fever. Ewing sarcoma and osteosarcoma typically do not occur in toddlers, and it is the long bones that are most often involved. Because of the girl's multiple lesions and the nonworrisome radiographic findings, you conclude that neither a benign nor a malignant tumor of bone is likely.

More and more, you are convinced that this patient has an unusual infection. (More and more, you feel like that Ancient Mariner of epic poetry-your search for a diagnosis like his voyage across a sea of unusual and inexplicable creatures and unexpected occurrences in "The Rime of the Ancient Mariner." Would the hero of Samuel Taylor Coleridge's puzzling 18th-century work know just how you feel as you confront this challenging investigation?)