We read with interest the important contribution of Carey et al.  to the debate concerning ultrasound lipodystrophy assessments.
They excluded the possibility of using ultrasonography to assess facial atrophy; in particular, they did not find a correlation with more established measures such as dual-energy X-ray absorptiometry (DEXA) and computed tomography (CT), or with subjective severity scores assessed by physical examination or patient reports. Although the use of ultrasonography in assessing lipodystrophy alterations has objective difficulties in terms of standardization, its accuracy in measuring changes in subcutaneous fat thickness (SFT) at the brachial, crural and malar levels has been demonstrated by Martinez et al. , Asensi et al.  and ourselves .
Carey et al.  chose the outer canthus of the right eye and the upper margin defined by malar bone as their reference point for the ultrasound determination of malar SFT, and this deserves some comment because, in our opinion, the correct way to determine the size of Bichàt's bulla and measure malar SFT is to use a nasogenian transversal scan from the malar bone to the skin (Fig. 1).
The reasons for this choice also include the clinical presentation of sunken cheeks, and after a long debate and a number of practical attempts with our radiologists, we believe that our scan is more representative of facial atrophy than the longitudinal image taken by Carey et al. .
Our reference point corresponds to the deepest point of Bichàt's bulla, which we think is the correct echographic reference point for measuring facial lipoatrophy whereas, in our experience, the topographical site used by Carey et al.  is too peripheral to guarantee a realistic description of fat loss.
In addition to this crucial technical point, some other considerations need to be made in this kind of investigation. First consideration concerns the patient's body mass index (BMI) because subcutaneous and visceral fat distribution is related to the BMI in the majority of cases, with lipoatrophy when the BMI is less than 27 kg/m2 and lipohypertrophy when the BMI is greater than 27 kg/m2[5,6]. It is also well known that the presentation of lipodystrophy is often different in male and female HIV patients , and there is still controversy concerning sex-related differences in body fat distribution .
Comparing ultrasonography with other tools, for example DEXA, are not necessarily appropriate because, by definition, DEXA cannot give any information about regional fat distribution, particularly facial lipoatrophy and moreover the simple DEXA evaluation of limb fat mass can be unreliable unless it is corrected by BMI.
Similarly, attempts to correlate ultrasound determinations with CT scans of body regions other than the malar region carry the same risk of inaccuracy, particularly for diagnosis of focalized lipoatrophy.
The lack of correlation between patient and doctor judgments and ultrasound determinations can be easily explained on the basis of the choice of the topographic reference point discussed above.
At the 5th International Workshop on Adverse Drug Reactions and Lipodystrophy in HIV (Paris, 2003), Milinkovic et al.  reported a good correlation between ultrasonography and CT or DEXA subcutaneous fat measurements at similar levels.
Although it has not yet been demonstrated that ultrasonography can assess lipodystrophy, the possibility of at least partly replacing expensive methods of measuring fat alterations such as DEXA and CT is too important to be abandoned without further investigations.
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