Marine-Lenhart Syndrome Masquerading as Ocular Myasthenia Gravis: A Case Revealed by Isolated Unilateral Ptosis

Graves’ disease (GD) is the leading cause of hyperthyroidism, with ophthalmic involvement occurring in up to 50% of cases (Graves’ orbitopathy, GO). Classical GO features include bilateral proptosis, lid retraction, and restrictive strabismus. Unilateral ptosis is an exceedingly uncommon presenting sign of Graves’ disease and poses a significant diagnostic challenge, frequently leading clinicians to prioritize neurological etiologies before the underlying thyroid autoimmune process is identified. We present a 34-year-old woman referred for progressive right-sided ptosis over six months, initially investigated for neurological causes. Ophthalmological assessment revealed mild right-sided proptosis and inferior scleral show contralateral to the ptotic lid, consistent with unilateral lid retraction masking asymmetric GO. Biochemical evaluation confirmed hyperthyroidism with a suppressed TSH, markedly elevated free T4 and T3, and positive thyroid-stimulating immunoglobulins (TSI) and thyrotropin receptor antibodies (TRAb). Thyroid ultrasound identified a diffusely enlarged gland with a 1.8 cm right lobe nodule. Tc-99m scintigraphy demonstrated diffusely increased uptake with a superimposed focus of relatively autonomous activity corresponding to the nodule, establishing the diagnosis of Marine–Lenhart syndrome the rare coexistence of Graves’ disease with an autonomously functioning thyroid nodule. Orbital MRI revealed asymmetric extraocular muscle enlargement bilaterally, right greater than left, confirming Graves’ orbitopathy as the cause of apparent unilateral ptosis. This case highlights two converging diagnostic challenges: the misclassification of contralateral lid retraction as unilateral ptosis, and the recognition of Marine–Lenhart syndrome a rare overlap of Graves’ hyperthyroidism with a coexisting autonomously functioning thyroid nodule (AFTN) found in fewer than 3% of Graves’ patients. The presence of Marine–Lenhart syndrome critically modifies the management strategy, particularly regarding radioiodine dosing, surgical planning, and the assessment of post-treatment euthyroidism.