Paradoxical Cortisol Response to Dexamethasone in Corticotroph Microadenoma: A Useful Feature of Underlying Cyclic Hormonogenesis

Cushing’s syndrome in early infancy due to isolated sporadic bilateral micronodular adrenocortical disease associated with myosin heavy chain 8 mutation: diagnostic challenges, too many!

Endogenous Cushing’s syndrome (CS) is rare in infancy. Bilateral micronodular adrenocortical disease (BMAD), either primary pigmented nodular adrenocortical disease or the non-pigmented isolated micronodular adrenocortical disease is an important aetiology of CS in this age group, which requires bilateral adrenalectomy for cure. BMAD may be isolated, or a component of Carney complex. Isolated sporadic BMAD without other systemic manifestations poses a diagnostic challenge. Paradoxical cortisol response to dexamethasone suggests, while adrenal histopathology and mutational analysis of the culprit genes confirm BMAD. BMAD was suspected in 6-year-old infant with midnormal adrenocorticotrophic hormone, inconclusive adrenal and pituitary imaging and paradoxical increase in cortisol following high dose of dexamethasone. Exome sequencing revealed heterozygous c.354+1G>C (5′ splice site) variant in the myosin heavy chain gene (MYH8), located in chromosome 17. This particular variant has not been reported in the literature. In view of suspected phenotype and its absence in the population databases, the variant was classified as pathogenic.