A Rare Triad: Pancytopenia and Hypothyroidism in a Genetically Confirmed Case of Trisomy 21

Trisomy 21 (Down syndrome) is frequently associated with haematological and endocrine abnormalities. We report the case of a 16-year-old female with genetically confirmed non-mosaic Trisomy 21 who presented with fever, cough, and loose stools. Clinical features included short stature, obesity, and microcephaly. Laboratory investigations revealed pancytopenia with haemoglobin 4.5 g/dL, leukocyte count 4200/mm³, and platelet count 1.0 lakh/mm³. Red cell indices showed microcytic hypochromic anemia (MCV 74 fL, MCH 19 pg, MCHC 26 g/dL), corroborated by peripheral smear and a raised reticulocyte count (4.1%). Thyroid function tests indicated severe hypothyroidism (TSH > 49.90 µIU/mL). Bone marrow aspiration demonstrated hypocellularity with erythroid suppression, without evidence of malignancy. The patient responded well to levothyroxine (Thyronorm 75 mcg/day) and one unit of packed red blood cell transfusion. This case highlights the need for routine thyroid assessment and bone marrow evaluation in Down syndrome patients with pancytopenia to ensure timely identification of comorbidities, improves quality of life and avoids unnecessary oncological workup.