A 15-year-old boy presented to the paediatrician with precocious puberty, hyperthyroidism, hyperprolactinaemia and large, asymmetric head.
Inspection of the skin showed “café-au-lait” spots located mainly on the back (Fig. 1) and left buttock.
Conventional radiography (CR) showed multiple bone lesions with a ground glass appearance in both femurs (Fig. 2, 3), left humerus (Fig. 4), right tibia and right talus (Fig. 5, 6). Bone scintigraphy showed multifocal tracer uptake in the axial and appendicular skeleton suggesting active osteoblastic activity (Fig. 7).
Magnetic Resonance Imaging (MRI) of the brain showed asymmetric expansion of the calvaria and facial bones with significant bone thickening. Lesions showed predominantly low, slightly inhomogeneous signal intensity on all pulse sequences (Fig. 8, 9, 10). The brain was normal (Fig. 8, 9). The orbits were small. (Fig. 10). However, there was no compression of the optic nerve (Fig. 10).
Based on the combination of clinical and imaging findings, the diagnosis of McCune-Albright syndrome (MAS) was made.
MAS is a genetic disorder characterized by a typical triad of symptoms: polyostotic fibrous dysplasia (FD), skin pigmentation (café-au-lait spots) and endocrinological disorders [1]. Gonadal dysfunction is considered to be the most common endocrine defect in females, resulting in precocious puberty and vaginal bleeding. However, Cushing syndrome, pituitary adenomas and hyperthyroidism are also reported [2]. MAS develops from activation of a post-zygotic, sporadic or somatic mutation of the GNAS1 gene with different clinical manifestations [3]. Affected children usually present with skeletal deformities and short stature, resulting from premature closure of the epiphyses.
FD is a tumour-like condition of the bone. Histologically it corresponds to immature bone with delicate trabeculae and interspersed fibrous matrix [4]. This makes the bone more prone to microfractures, repetitive remodelling and subsequent deformation [5]. FD associated with MAS usually affects multiple bones and leads more frequently to complications such as fractures, skeletal deformities or limb-length discrepancies. It affects most commonly the femora, tibiae, pelvis, skull and ribs. Imaging features of FD may vary from either completely radiolucent lesions, sclerotic delineated radiolucent lesions or lesions with a ground-glass matrix appearance. In case of disease progression, bowing of the proximal femora (coxa vara) may occur due to multiple fractures and repetitive remodelling, resulting in the so-called shepherd’s crook deformity. [4, 6].
Conventional radiography (CR) is usually sufficient to make a reliable diagnosis.
Bone scintigraphy may reveal increased osteoblastic activity in affected bones. It is particularly useful to assess multifocality.
Computed tomography (CT) is usually not mandatory, but may be used to evaluate the precise extent of FD and potential compression of adjacent structures in complex anatomical structures such as the facial bones, skull base and the axial skeleton. However, due to high radiation dose, the use of CT should be considered with caution.
Particularly in the paediatric population, MRI is the preferred technique for evaluation of the lesion extent in the skull bones. Bone expansion may cause compression of adjacent structures, such as the optic nerve, resulting in visual disturbances. Osteotomy of the involved bones should be considered in this scenario.
Malignant transformation of bone lesions is rare.
Paget's disease may appear similar on imaging but is seen in older patients. Association of FD and intramuscular myxoma is known as Mazabraud syndrome.
Polyostotic fibrous dysplasia related to McCune-Albright Syndrome
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1. X-ray and bone scan: Multiple skeletal changes are noted, primarily with the following characteristics:
2. Skin examination: “Café-au-lait” spots with irregular shapes and clear borders on the back and left buttock.
3. Head MRI: Notable pituitary enlargement, indicating hyperfunction of the pituitary gland, consistent with clinically detected hyperprolactinemia. Overall brain parenchyma is structurally intact, but head circumference is relatively large.
4. Additional findings: Clinical evaluation reveals hyperthyroidism and signs of precocious puberty in a male (early sexual development).
Based on the patient’s history, physical examination, and imaging findings, the following differential diagnoses are considered:
Considering the patient’s age, signs of precocious puberty, endocrine hyperfunction (hyperthyroidism, hyperprolactinemia), polyostotic fibrous dysplasia on imaging, and café-au-lait spots, the most likely diagnosis is:
McCune-Albright Syndrome (MAS).
Diagnostic criteria include:
If further confirmation of the pathological nature or genetic features is needed, genetic testing (GNAS1 mutation) or bone biopsy may be performed. However, the clinical and imaging findings in this case are quite typical.
1. Endocrine management:
2. Bone lesion management:
3. Rehabilitation and exercise guidance:
Disclaimer: This report is for medical reference only and should not replace in-person clinical evaluations or the judgement of qualified healthcare professionals. If you have any questions or if symptoms change, please consult a specialist without delay.
Polyostotic fibrous dysplasia related to McCune-Albright Syndrome
