Dropped Head Syndrome Secondary to Danon Disease: A Case Report.

Dropped head syndrome (DHS) is characterized by neck extensor muscle weakness, which may be isolated or secondary to another neurologic diagnosis. DHS, due to lysosomal storage disorders, has not been reported in the literature. We present a 21-year-old male who had complaints of slowly worsening difficulty swallowing for the past eight years, along with difficulty keeping his head erect. His past medical history was significant for apical hypertrophic cardiomyopathy (HCM), and he had a history of sudden cardiac death in his immediate family. Clinical examination was significant only for neck extensor muscle weakness. His laboratory investigations were unremarkable, save for a significantly elevated creatine kinase (CK). Finally, whole exome sequencing identified a hemizygous stop gain variant in the lysosome-associated membrane protein 2 (LAMP-2) gene, pointing to a diagnosis of Danon disease (DD). DD is a rare, X-linked, inherited disease, due to a defect in the LAMP-2 gene that disrupts lysosomal autophagy. It is characterized by a triad of HCM, skeletal myopathy, and intellectual disability. Males typically suffer a more severe phenotype, and the cardiac disease drives its prognosis. Management involves regular cardiac monitoring, with appropriate physical therapy for myopathy and multidisciplinary treatment for intellectual disability. We suggest that DD be considered in the differential diagnosis for patients with HCM and elevated CK.