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. Author manuscript; available in PMC: 2016 Sep 1.
Published in final edited form as: Clin Nucl Med. 2015 Sep;40(9):727–729. doi: 10.1097/RLU.0000000000000851

Assessing Cutaneous Psoriasis Activity Using FDG-PET

Nonattenuation Corrected Versus Attenuation Corrected PET Images

Anshika Bakshi *,†, Saeid Gholami ‡, Abass Alavi ‡, Joel M Gelfand †, Junko Takeshita †
PMCID: PMC4589162  NIHMSID: NIHMS724343  PMID: 26053710

Abstract

Psoriasis is a chronic inflammatory skin condition characterized by well-circumscribed erythematous plaques with thick silvery scale. Infiltration of inflammatory cells such as lymphocytes, neutrophils, and macrophages and epidermal cell proliferation within psoriatic lesions may result in selective FDG accumulation. We present a 55-year-old patient with a 30-year history of psoriasis. Nonattenuation corrected PET/CT images demonstrated significant cutaneous FDG uptake corresponding to clinically apparent psoriatic lesions. However, in attenuation corrected (AC) FDG-PET images, the signal was substantially diminished and minimally detectable. Nonattenuation corrected FDG-PET images may be useful and preferable to AC images in assessing skin inflammation in psoriasis.

Keywords: Psoriasis, skin, fluorodeoxyglucose, positron emission tomography, non-attenuation corrected, attenuation corrected

FIGURE 1.

FIGURE 1

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A 55 year-old male patient with 30-year history of psoriasis treated with intermittent topical steroids until 2 weeks before PET-CT scan. The patient had severe psoriasis as indicated by 25% body surface area involvement, Psoriasis Area and Severity Index of 12.2, and Physician Global Assessment of 2.7 (induration, 2; erythema, 3; and scale, 3).1–5 Patient’s buttocks and posterior thighs show scattered psoriatic plaques. Black arrows point to clinically apparent psoriasis that showed FDG uptake in PET images. White arrows indicate areas without corresponding FDG uptake in PET images.

FIGURE 2.

FIGURE 2

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Increased FDG uptake in the skin detected by nonattenuation corrected (NAC) PET images is visualized in the posterior view of the 3-dimensional maximum intensity projection (MIP) image (AI) as indicated by black arrows and in coronal (AII) and trans-axial views (AIII). Cutaneous FDG uptake is minimally detectable in the posterior view of the attenuation corrected (AC) MIP (BI), coronal (BII), and axial (BIII) images. Increased FDG uptake as seen in NAC images corresponds with many clinically apparent skin lesions. However, there are also visible psoriatic plaques that are not associated with detectable FDG uptake in either corrected or uncorrected PET images (Fig. 1, white arrows). This discrepancy suggests limitations in the ability to identify active skin inflammation by clinical examination alone. Detection of cutaneous FDG uptake has been reported in cases such as squamous cell carcinoma,6 infection by Mycobacterium avium complex7 and herpes zoster,8 and variants of cutaneous T-cell lymphoma.9,10 Moreover, 2 reports have documented FDG uptake suggesting skin inflammation in psoriasis patients using AC FDG-PET images,11,12 and a single report has shown that the metabolic volume product of psoriatic lesions (the product of the mean standard uptake value [SUV] of all psoriatic lesions and total volume of psoriatic plaques [mL]) can be used to objectively quantify overall psoriasis activity as a biologic marker.13 As GLUT-1 has been reported to be upregulated in the epidermis of psoriatic lesions,14 FDG signal in psoriatic plaques may be attributable to uptake by proliferating keratinocytes in the epidermis in addition to inflammatory cells. The use of NAC FDG-PET images for identification of cutaneous inflammation has not been well described in the literature. Several studies report similar sensitivity between NAC and AC FDG-PET images for detection of various noncutaneous tumors.15–17 On the other hand, lung nodules,18 small pulmonary metastases of breast cancer,19 and superficial lymphoma20 lesions have been suggested to be more readily detectable by NAC images than by AC images. This superiority of NAC over AC may be due to lower contrast in AC images, which can be attributed to noise from transmission measurement, inhomogeneity of data transmission, and patient motion between emission and transmission scans.20 In our case report, we show that cutaneous inflammation in patients with psoriasis may be detected by FDG-PET imaging and suggest that NAC PET images may prove to be superior to AC images in identifying actively inflamed psoriatic skin lesions.

Acknowledgments

Conflicts of interest and sources of funding: Funding sources include the National Heart Lung Blood Institute grant R01 HL111293 and National Institute of Arthritis and Musculoskeletal and Skin grant K24-AR064310 (Principal Investigator: Dr. Joel M. Gelfand), AbbVie Inc. grant to Dr Joel M. Gelfand, National Institutes of Health Training Grant 2T32 AR 7465–31 (Anshika Bakshi), and Dermatology Foundation Career Development Award (Dr. Junko Takeshita).

Financial disclosures: Dr. Gelfand served as a consultant for Abbvie, Amgen Inc., Celgene Corp, Eli Lilly, Merck, Janssen Biologics (formerly Centocor), Novartis Corp, and Pfizer Inc., receiving honoraria; had grants or has pending grants from Abbvie, Amgen Inc., Eli Lilly, Genentech Inc., Novartis Corp, and Pfizer Inc.; and received payment for continuing medical education work related to psoriasis. Dr. Takeshita has received payment for continuing medical education work related to psoriasis.

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