The herculean illusion: congenital hypothyroidism masquerading as muscular dystrophy

We report a 21-year-old man, born out of non-consanguineous parentage, who presented with motor predominant developmental delay, intellectual disability, poor scholastic performance, lethargy, easy fatigability, and gradually progressive proximal muscle weakness with striking muscle enlargement since childhood, mimicking muscular dystrophy. Examination revealed coarse facies, macroglossia, dry scaly skin, and symmetrical hypertrophy of limb and shoulder girdle muscles, producing a "Herculean" appearance. Neurological evaluation demonstrated pseudohypertrophy with percussion-induced transient mounding and delayed tendon reflex relaxation. Investigations confirmed severe hypothyroidism with markedly elevated muscle enzymes, while MRI showed diffuse muscle enlargement with myoedema but without fatty infiltration. These clinical and radiological findings established a diagnosis of Kocher-Debré-Semelaigne/Hoffmann's syndrome. Thyroxine replacement resulted in significant improvement. This case underscores hypothyroidism as a potential reversible endocrine myopathy that can masquerade as muscular dystrophy. Recognition of characteristic systemic, neurological, and imaging features prevents unnecessary invasive or genetic testing and highlights the importance of timely hormone replacement therapy.