Puzzler: Rash, fever, and pharyngitis in an adolescent: Wait! Whose hoofbeats are those?

A Monday morning in September has come galloping in after a relatively quiet weekend, bringing with it to your office a 17-year-old Caucasian boy for evaluation of a developing rash on his hands and feet. Your patient had been in his customary good health until the preceding Friday, when he developed a fever of 103° F and myalgia that he considered, at times, severe and that was not fully relieved by acetaminophen or ibuprofen. Yesterday, he developed a sore throat and the rash and went to an urgent care center. There, he was told he likely had coxsackievirus infection.

The boy's parents told you this when they called you yesterday evening; from their description of the rash and sore throat, and knowing that you've been seeing cases of coxsackie, you agreed with the diagnosis made by the urgent care physician. This morning, however, they called again-to tell you that the character and distribution of the rash had changed. You advised them to bring their son in for examination.

Hands and feet get your attention This boy has been your patient since birth. The medical history is remarkable for congenital absence of the gallbladder, a condition discovered two years ago by ultrasonography that was performed as part of an evaluation of severe right-upper-quadrant pain, which resolved. An inguinal hernia was repaired at age 11 years. The patient has no allergies. The travel history is significant for his having spent most of the past summer in a mountain resort area of eastern Pennsylvania-the Poconos-as well for time spent in Belgium and Israel the same season.

On physical exam, the patient appears weak and ill, but not toxic. Temperature is 103.2° F; heart rate, 86/min; and respirations, 20/min. You note severe purulent tonsillopharyngitis, with petechial spots on the palate and gums, two sores on the palate, and some painful submandibular adenopathy, but the patient displays full range of motion of the neck. The sclera of the right eye is slightly injected, without discharge. The chest is clear; heart rate and rhythm are regular, and no murmurs are heard. The abdomen is soft, without hepatosplenomegaly or masses. Pubertal development is Tanner stage 5.

You note large, macular, red to purple, blanching lesions on the palms that extend to the wrists, with a few lesions as far proximally as the elbows. Tiny, macular, pink, blanching lesions can be seen on a small area of the right forearm. The rash on the feet is similar to what you see on the hands, and is beginning to extend to the ankles. All areas of the rash are blanching; none are palpable. You do not see any rash on the trunk. Skin turgor is good.

In light of the tonsillitis and rash, you order a number of laboratory tests: STAT CBC and sodium; a full chemistry panel; serology studies for Epstein-Barr virus infection, measles, Rocky Mountain spotted fever (RMSF), and ehrlichiosis; blood cultures; and a rapid antigen test and culture for streptococcal pharyngitis. Immediately, you see that the rapid strep test is negative, so you send the patient home to await the other results.

Results of the CBC return first, later that afternoon: the white blood cell count is 15.1 × 10³/μL, with a differential of 68% polymorphonuclear cells, 27% bands, 4% lymphocytes, and 1% monocytes; hemoglobin, 15.5 mg/dL; hematocrit, 44.7; and platelet count, 100 × 10³/μL. A slight number of Döhle bodies are noted on the slide. The sodium level is 134 mmol/L.

Considering what you've found-high WBC count, slightly low platelet count, slightly low sodium level, and blanching, macular rash mostly on the palms, wrists, and soles-you feel that telephone consultation with an infectious disease specialist is warranted. Because you have a high index of suspicion for RMSF and ehrlichiosis, and because delaying treatment could increase the risk of morbidity, even death, you start the patient on doxycycline that evening and prepare to follow up in the morning.