The great mimic: Unmasking congenital hypothyroidism in an adult presenting with features of mucopolysaccharidosis

ABSTRACT A 35-year-old male patient with a history of global developmental delay and intellectual disability presented with progressive vision loss, weight gain, lethargy, and disproportionate short stature. Physical examination revealed obesity (body mass index: 34 kg/m 2 ), macroglossia, abdominal distension, hepatomegaly, and bilateral keratoglobus. Laboratory tests confirmed severe hypothyroidism, with a thyroid-stimulating hormone (TSH) level of 170 µIU/mL, low triiodothyronine (T3) and thyroxine (T4), and significantly reduced insulin-like growth factor 1 (IGF-1) levels. Imaging studies raised suspicion of mucopolysaccharidosis (MPS); however, genetic testing for MPS was negative. The patient was treated with levothyroxine, leading to notable symptomatic improvement, normalization of thyroid hormone levels, and a reduction in TSH to 70 µIU/mL within one week. After three months of treatment, the patient showed further improvement, including reduced macroglossia, decreased abdominal distension, and resolved hepatomegaly. He was scheduled for left-eye keratoplasty and discharged in stable condition. This case highlights a rare presentation of longstanding, untreated congenital hypothyroidism mimicking MPS, and posing a significant diagnostic challenge.