Hand, Foot, and Mouth Disease Associated With Transient Hyperphosphatasemia

A majority of pediatric outpatient practice involves managing familiar diseases that present in familiar ways. Occasionally, a familiar disease presents uniquely, which adds a diagnostic challenge and enhances the clinical experience of the clinician. We describe an 18-month-old male who presented to the clinic with a familiar disease but with unique additional findings. The patient had a one-day history of rash, subjective fever, and several episodes of non-bloody diarrhea. The rash included petechial lesions across his abdomen, groin, back, arms, and legs, as well as vesicular lesions in the mouth and on the palms and soles. A tentative diagnosis of hand, foot, and mouth disease (HFMD) was made. However, the presence of petechiae prompted further laboratory evaluation, including a complete blood count (CBC) and comprehensive metabolic panel (CMP). The CBC was unremarkable, but the CMP revealed an abnormally high serum alkaline phosphatase (ALP) level of 1,353 U/L (normal range: 53-128 U/L). The patient was subsequently diagnosed with an atypical presentation of HFMD associated with transient hyperphosphatasemia (TH). TH is characterized by a benign increase in serum alkaline phosphatase levels with an absence of liver or bone diseases. TH is usually clinically silent. Clinicians should consider the possibility of TH in pediatric patients who are found incidentally to have an elevated ALP, especially with a concomitant viral infection. An awareness and understanding of TH will prevent unnecessary additional testing and avoid undue parental anxiety.