GBM

GBM has two critical meanings in medical education: (1) Glomerular Basement Membrane: a specialized extracellular matrix composed of type IV collagen, laminin, nidogen, and perlecan, located between the glomerular endothelium and podocytes. The GBM is critical for the glomerular filtration barrier (prevents passage of large molecules and blood cells while allowing water and small solutes). Damage to GBM occurs in anti-GBM disease (Goodpasture syndrome), an autoimmune disorder where autoantibodies target the alpha-3 chain of type IV collagen; presents with rapidly progressive glomerulonephritis (crescent formation on biopsy) and pulmonary alveolar hemorrhage (hemoptysis, pulmonary infiltrates, diffuse alveolar hemorrhage pattern). Anti-GBM testing (serology and kidney biopsy immunofluorescence showing IgG/complement linear deposition along GBM) is diagnostic. Treatment: plasmapheresis (remove circulating antibodies) + immunosuppression (corticosteroids, cyclophosphamide). (2) Glioblastoma Multiforme: the most common and aggressive primary brain malignancy (WHO Grade IV glioma), arising from glial cells (astrocytes). Highly malignant with poor prognosis (median survival ~15 months even with treatment). Presents with progressive neurologic deficits, seizures, headache, and focal deficits (depending on tumor location). Risk factors: prior brain radiation, neurofibromatosis type 1. Diagnosis: MRI (contrast-enhancing mass with central necrosis, surrounding edema), biopsy for histopathology. Molecular features: IDH mutation status (IDH-mutant GBM has better prognosis), MGMT methylation status (predicts alkylating agent response). Treatment: maximal safe surgical resection + concurrent chemoradiation (temozolomide) + adjuvant temozolomide (Stupp protocol). On boards, clarify context: nephrology questions about GBM likely refer to glomerular basement membrane; neuro-oncology questions refer to glioblastoma. Both are high-yield.