McCUNE-ALBRIGHT SYNDROME
 
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    McCUNE-ALBRIGHT SYNDROME

     

    DEFINITION:

    A syndrome characterized by fibrous dysplasia of the skeletal system, cafe-au-lait spots, and endocrine dysfunction.

    EPIDEMIOLOGY:

    • incidence: rare
    • age of onset:
      • mean - 3 years
    • risk factors:
      • familial - ?autosomal dominant
        • chrom.#: 20q13.2
        • gene: ?

    PATHOGENESIS:

    1. Background

    • first described in 1937 by Albright et al.
    • considered a pseudo or incomplete precocious puberty
      • gonadotropin-independent
      • development of some secondary sexual characteristics
        • isosexual or heterosexual
      • no maturation of gonads
    • not a hypothalamic disorder: the endocrine dysfunction appears to arise from autonomous hyperfunction of the involved glands:

    1. Thyroid

    • multinodular goiters -> increased T3 -> decreased TSH

    2. Adrenal

    • bilateral nodular adrenocortical hyperplasia -> increased cortisol -> decreased ACTH

    3. Pituitary

    • plurihormonal-secreting adenoma -> increased growth hormone

    4. Ovaries

    • luteinized follicle cysts function independently of gonadotropins -> increased estradiol (levels of estradiol may correlate with size of cysts) -> decreased FSH and LH
    • when bone age reaches the usual pubertal range, may get true (gonadotropin-dependent) precocious puberty
    • functioning ovarian cysts often disappear spontaneously

    CLINICAL FEATURES:

    1. Endocrine Dysfunction

    1. Hyperthryroid

    • M = F
    • thyroid - goiter present and multinodular
    • clinical hyperthyroidism is uncommon

    2. Cushing Syndrome

    • may occur in early infancy before onset of precocious puberty
    • adrenals - bilateral nodular adrenocortical hyperplasia

    3. Acromegaly

    • M = F
    • increased rate of growth even in absence of precocious puberty
    • less than 50% have a demonstrable plurihormonal-secreting adenoma of the pituitary

    4. Precocious Pseudopuberty

    • F > M
    • mean age of onset at 3 years
      • vaginal bleeding may begin as early as 4 months (may be the first manifestation of the syndrome)
      • secondary sexual characteristics may develop as early as 6 months
    • precocious pseudopuberty as puberty is gonadotropin-independent
    • in adolescence may have regular puberty and pregnancy is possible

    2. Skeletal Dysfunction

    1. Polyostotic Fibrous Dysplasia

    • fractures and deformities of the long bones

    3. Integument

    1. Cafe-au-lait Spots

    • occur on neck, face, back, shoulders
    • may be evident at birth

    INVESTIGATIONS:

    1. Serum

    • thyroid - mildly elevated T3, decreased TSH
    • adrenal - elevated cortisol, decreased ACTH
      • adrenal function not suppressed by dexamethasone
    • pituitary - elevated growth hormone and prolactin
    • ovaries - estradiol levels normal to markedly elevated and may be cyclic
    • suppressed levels of LH & FSH
    • no response to LHRH stimulation

    2. Imaging Studies

    1. Ultrasound

    • ovarian cysts
    • nodular adrenal hyperplasia

    2. Skeletal X-Rays

    1. Polyostotic Fibrous Dysplasia

    • widespread cystic bony changes
    • bony lesions in the base of the skull
    • fractures and deformities of the long bones
    • advanced bone age

    MANAGEMENT:

    1. Hyperthyroidism

    • Medical
    • Radiation
    • Surgical

    2. Cushing Syndrome

    • Surgical - adrenalectomy

    3. Acromegaly

    • octreotide - long-acting somatostatin inhibitor

    4. Precocious Puberty

    • functioning ovarian cysts often disappear spontaneously
    • no response to LHRH analogs
    • testolactone may decrease estradiol secretion by interfering with an aromatase inhibitor that interferes with the final step of estrogen biosynthesis


     

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    Pediatric Database - McCUNE-ALBRIGHT SYNDROME

     

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