741 Color Doppler sonography (CDS) is increasingly being recommended as a first-line investigative tool in differ- ential diagnosis of thyrotoxicosis (1). We report the atyp- ical findings of CDS in a case of apathetic thyrotoxicosis. A 75-yr-old man presented with a 6-month history of anorexia, weight loss of 6-7 kg, lethargy, and extreme weakness of limbs. One month prior to presentation the patient gave history of progressive dyspnea on exertion without associated orthopnea and other cardiovascular symptoms. There was no history of psychiatric complaints or similar illness in family. On examination, the patient appeared lethargic and uncommunicative with a pulse rate of 108 beats/min and blood pressure of 130/86 mmHg. The skin was dry and there was no evidence of pedal edema. The thyroid gland was not enlarged and there was no hand tremor or ocular signs of hyperthy- roidism. Marked weakness of proximal muscle groups of all limbs and wasting of small muscles of hand were not- ed. Cardiovascular system examination did not reveal any significant abnormality. Investigations revealed hemo- globin: 13.6 g/dl and chest X-ray and electrocardiogram were normal. Thyroid function tests revealed evidence of hyperthyroidism with suppressed TSH<0.01 mIU/l (0.4- 4.2 mIU/l) and elevated T 3 : 368 ng/dl (70-190 ng/dl) and T 4 : 14.2 μg/dl (5-11 μg/dl) with positive anti-thyroid per- oxidase antibodies. CDS of thyroid gland was performed using Philips Envi- sor ultrasound machine with 7.5 MHz linear probe. The thyroid gland was of normal size (calculated volume: 14.6 cc) with mild increase in intraparenchymal vascularity and peak systolic velocity (PSV) of inferior thyroid artery (ITA) was 14 cm/sec on left side and 18 cm/sec on right side. 99mTc pertechnate scan showed increased uptake of tracer confirming the diagnosis of apathetic thyrotoxico- sis. The patient was treated with Carbimazole 30 mg per day in divided doses and after 4 weeks was relieved of his symptoms and gained 3 kg in weight. Apathetic thyrotoxicosis is a distinct subset of hyperthy- roidism often missed due to absence of typical symp- toms and signs. The salient features are apathy, depres- sion, weight loss, muscle weakness and wasting. Note- worthy is the absence of hyperkinetic motor activity, tremors, and ocular signs typical of Graves’ disease. The thyroid gland if palpable is minimally enlarged. The di- agnosis is confirmed by thyroid function tests and pertechnetate scan. CDS is an instant, non-invasive method of measuring tis- sue vascularization and blood flow. CDS of thyroid gland can give valuable information about underlying thyroid functional status and is useful in differentiating destruc- tive thyrotoxicosis from Graves’ thyrotoxicosis (2). Graves’ disease patients typically have markedly in- creased intraparenchymal vascularity, so called “thyroid inferno” and increased PSV of ITA (3). Based on various studies using CDS of thyroid, it is even proposed that CDS should be the first investigation of thyrotoxicosis and may replace nuclear imaging in future (4). In the case described, the diagnosis of apathetic thyro- toxicosis was established by typical presentation, absent hyperkinetic features, biochemical hyperthyroidism, and increased tracer uptake on pertechnetate scan. Howev- er, the CDS findings in the case were not suggestive of hyperthyroidism, giving a false negative test result. Al- though color Doppler can reliably differentiate hyperthy- roidism from thyrotoxicosis, this has not been seen in the case described of apathetic thyrotoxicosis. Extensive lit- erature search revealed no result regarding the role of CDS in apathetic thyrotoxicosis. This may be because of uncommon occurrence of apathetic thyrotoxicosis and lack of awareness of CDS role in evaluation of thyrotoxi- cosis. Kurita S. et al. in their study of 75 patients with thy- rotoxicosis demonstrated that CDS had a sensitivity of 84% and specificity of 90% in differential diagnosis of thy- rotoxicosis (5). Even though CDS of thyroid gland is a very informative technique, it only gives indirect evidence of functional thyroid status. There is considerable overlap between patients with mild hyperthyroidism and goitrous hypothyroidism exposing the limitations of this method. To the best of our knowledge, this is the first case to re- port CDS findings in apathetic thyrotoxicosis. We believe that future studies of CDS of thyroid gland should include all subsets of disease including neonatal/childhood Graves’ disease and apathetic thyrotoxicosis. This may be more useful in defining the role of CDS as an alternative to nuclear imaging in the evaluation of thyrotoxicosis. Accepted January 7, 2008. Apathetic thyrotoxicosis – Can color Doppler sonography help? J. Endocrinol. Invest. 31: 741, 2008 ©2008, Editrice Kurtis LETTER TO THE EDITOR K.V.S. Hari Kumar and K.D. Modi Endocrinology, Medwin Hospitals, Hyderabad, India REFERENCES 1. Erdo ˘ gan MF, Anil C, Cesur M, Bas ¸kal N, Erdo ˘ gan G. Color flow Doppler sonography for the etiologic diagnosis of hyperthyroidism. Thyroid 2007 Mar, 17: 223-8. 2. Ota H, Amino N, Morita S, et al. Quantitative measurement of thy- roid blood flow for differentiation of painless thyroiditis from Graves’ disease. Clin Endocrinol (Oxf) 2007, 67: 41-5. 3. Macedo TA, Chammas MC, Jorge PT, et al. Reference values for Doppler ultrasound parameters of the thyroid in a healthy iodine non deficient population. The Br J Radiol 2007, 80: 625-60. 4. Bogazzi F, Vitti P. Could improved ultrasound and power Doppler replace thyroidal radioiodine uptake to assess thyroid disease? Nat Clin Pract Endocrinol Metab 2007, Nov 6 [Epub ahead of print]; doi: 10.1038/ncpendmet0692. 5. Kurita S, Sakurai M, Kita Y, et al. Measurement of thyroidal blood flow area is useful for diagnosing the cause of thyrotoxicosis. Thyroid 2005, 15: 1249-52. © 2008, Editrice Kurtis FOR PERSONAL USE ONLY