Hyperpigmented patches on the neck, shoulder, and back
During a routine examination, a 17-year-old boy was noted to have unilateral hyperpigmented patches on his left neck, shoulder, and back. The lesions had been present since birth, had not changed in size or color, and were asymptomatic. His mother had noted an increase in the size of his left jaw starting at age 1.
The hyperpigmented patches had irregular borders (Figure 1). The skin was otherwise clear. Laboratory testing from 5 years earlier showed normal levels of dehydroepiandrosterone, prolactin, parathyroid hormone, thyroxine, and thyroid-stimulating hormone. Computed tomography showed a “ground-glass” appearance of the bones at the base of the skull, consistent with polyostotic fibrous dysplasia (Figure 2).
,Q: Which is the most likely diagnosis?
- Neurofibromatosis
- Congenital melanocytic nevus
- McCune-Albright syndrome
- Tuberous sclerosis
A: This patient had typical features of McCune-Albright syndrome (or Albright syndrome), the classic triad of fibrous dysplasia of bone, large unilateral café-au-lait macules or patches, and precocious puberty or other endocrinopathy.1 The syndrome is rare, with an estimated prevalence of 1/100,000 to 1/1,000,000.2 It results from somatic mutation of the GNAS gene (chromosome 20q13) during embryonic development, which causes constitutive activation of intracellular cyclic adenosine monophosphate (cAMP) signaling and cellular dysplasia.3
THE DIAGNOSIS IS CLINICAL
McCune-Albright syndrome is a clinical diagnosis based on the presence of at least two features of the classic triad.1,4
Other conditions, such as neurofibromatosis, also cause café-au-lait macules in children; but the lesions of McCune-Albright syndrome are fewer in number, larger, and darker and may follow Blaschko lines, with a linear or segmental configuration.5 McCune-Albright lesions tend to have jagged, “coast-of-Maine” borders, as opposed to the smoother “coast-of-California” borders of the lesions of neurofibromatosis.1
Nevertheless, because café-au-lait macules of McCune-Albright syndrome are sometimes indistinguishable from those of neurofibromatosis, the endocrine and skeletal manifestations are essential to making the diagnosis.5
