McCune-Albright Syndrome. Case Report, a challenge for the neuroaxial and regional anesthetic approach.

Abstract

Definition: A rare, non-hereditary, and sporadic genetic disorder defined by a pattern of somatic mosaicism resulting from a postzygotic mutation in the early stages of embryogenesis. With an estimated prevalence between 1:100,000 and 1:1,000,000, the disease classically manifests through the triad of polyostotic fibrous dysplasia (FD), hypermelanotic skin lesions, and hyperfunctional endocrinopathies. The severity of the clinical phenotype is intrinsically linked to the timing of the mutation: an earlier alteration leads to a wider distribution of mutated cells across the various germline cells, resulting in greater multisystem involvement.

Molecular and Genetic Pathophysiology: Caused by gain-of-function mutations in the GNAS gene (chromosome 20q13.32), which encodes the alpha subunit of the stimulatory G protein. The pathogenic variants are missense mutations concentrated in two critical regions: codon p.Arg201 (Exon 8) in 95% of cases and codon p.Gln227 (Exon 9).

Clinical Manifestations: The Multidisciplinary Spectrum: Hypermelanotic macules are usually the earliest clinical sign. They are characterized by: - ​​Irregular borders: "Costa di Maine" pattern (jagged borders). - Blaschko distribution: Reflects embryonic cell migration. - Midline sparing: The lesions terminate abruptly along the sagittal axis.

Fibrous Dysplasia (FD) and Bone Progression: FD replaces bone architecture with fibrous stroma and immature trabeculae. A vital prognostic concept is the window of progression: most clinically significant skeletal lesions appear before age 5, consolidate by age 10, and it is exceptional for new lesions to appear after age 15.

Complications: Chronic bone pain, pathological fractures, and deformities such as femoral shepherd's crook. In the craniofacial region, bone expansion can compromise the optic and auditory canals, especially if excess Growth Hormone (GH) is present.

Diagnosis: Clinically, it requires at least two typical characteristics. In the case of a solitary fibrous dysplasia lesion, molecular confirmation is imperative.

Case presentation:

A 29-year-old female patient with a history of McCune-Albright syndrome, polyostotic fibrous dysplasia, osteoporosis, and primary hypothyroidism. She reports having been treated since birth at the National Institute of Pediatrics (INP), where she received follow-up and management until reaching adulthood, at which point she was transferred to the National Institute of Medical Sciences and Nutrition Salvador Zubirán (INCMNSZ). The INR referred her to the National Institute of Rehabilitation (INR) for functional evaluation and follow-up due to multiple well-defined lytic lesions in the skull, pelvis, thoracic and pelvic limbs, particularly with severe deformity in both femurs and the right tibia. A corrective osteotomy of the posterior thigh was planned and proposed (IV sedation, mixed neurovascular block, popliteal sciatic and adductor canal blocks). This resulted in neuropraxia of the right tibial nerve, and a revision of the osteotomy was scheduled (IV sedation, subarachnoid neurovascular block, and transgluteal sciatic block). X-ray images, CT reconstruction, and surgical procedure images are available.