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Brief Communication

Clinical utility of 18 Fluorodeoxyglucose (FDG)-PET/CT scans in patients with suspect ocular tuberculosis

Mehta, Salil

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Indian Journal of Ophthalmology: October 2013 - Volume 61 - Issue 10 - p 603-605
doi: 10.4103/0301-4738.121091
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Abstract

Systemic imaging of patients with suspect ocular tuberculosis forms a crucial part of the evaluation. Modalities used include chest X-rays (that image the parenchyma) and computed tomography (CT).

Modalities used include chest x-rays (that image the parenchyma) and computed tomography (that image both the parenchyma and the mediastinum). Recent reports have suggested a role for 18 fluorodeoxyglucose (FDG)-positron emission tomography (PET)/CT due to more extensive and potentially more sensitive imaging.[1] We report on the clinical utility of 18 FDG-PET/CT in two patients.

Case Reports

Case 1

A 38-year-old female patient presented with a history of recurrent attacks of bilateral pain, redness, and visual loss since the past 2 years. Previous investigations included a complete blood count and a mantoux test, and had 1 month ago, been started on empirical antitubercular therapy (based on a “positive” result) along with topical corticosteroid therapy.

Her best corrected visual acuity was counting fingers at 2 meters in the right eye and counting fingers close to her face in her left eye. Slit lamp examination of her right eye revealed fresh nongranulomatous keratic precipitates with a severe anterior chamber reaction (cells 2+, flare 2+). The anterior chamber was shallow with 360 ° adherence of the iris to the capsule of a complicated cataract. There was significant forward bowing of the iris diaphragm with peripheral anterior synechiae. There was significant iris neovascularization seen. Similar findings were seen in the left eye but there was a more marked shallowing of the anterior chamber with extensive irido-corneal touch. There was no fundal view but an ultrasound showed an anatomically normal posterior segment. The intraocular pressure was 10 and 8 mmHg.

A repeat mantoux test showed induration of 21×18 mm. Her total and differential blood counts, tests for serum creatinine, serum calcium, serum angiotensin converting enzyme, and serological tests to detect HIV infection were normal.

A 18 FDG-PET scan revealed a metabolically active, large 3×2.2 cm heterogenous right supraclavicular, partially necrotic, lymph node (SUV max 6.6) [Figure 1a, 1b]. There were metabolically active lymph nodes in the chest (right paratracheal [1.0×1.5 cm; SUV max 5.5] and subcarinal [1.5 × 2.6 cm; SUV max 7.7]) but the lungs were clear. Minimally metabolically active nodes were seen in the axilla.

Figure 1
Figure 1:
(a) Fused axial PET/CT image of the cervical region of Case 1 showing the right supraclavicular lymph node (arrow) (b) Fused PET/CT coronal scan of Case 1 showing the right supraclavicular lymph node(arrow)

She underwent ultrasound guided fine needle aspiration cytology of the right cervical lymph node that was highlighted on the PET/CT scan. The microscopic examination revealed caseating granulomas suggestive of tuberculosis. A Transcription Mediated Amplification (TMA) polymerase chain reaction (PCR) for mycobacterium tuberculosis genome had a positive result.

She was started on a standard four drug antitubercular regimen along with topical and periocular steroid therapy. On last follow up one month later there was a marked reduction of clinical anterior chamber activity.

Case 2

A 58-year-old female patient presented with a history of persistent pain, redness accompanied by bilateral visual loss since the past one and one half years. Previous significant medical history included surgery for pituitary macroadenoma 26 years ago. Previous investigations included a mantoux test that had been reported as “positive” but the patient had declined to start antitubercular therapy.

Her best corrected visual acuity was counting fingers at 6/12 in the right eye and 6/36 in her left eye. Slit lamp examination of her right eye revealed multiple fresh nongranulomatous keratic precipitates with a severe anterior chamber reaction (cells 2+, flare 2+). The anterior chamber had a normal depth but there were extensive posterior synechiae with a complicated cataract. similar findings were seen in the left eye.

The disc and the retina were normal in either eye. The intraocular pressure was 10 and 12 mmHg.

Systemic evaluation revealed palpable cervical and axillary lymph nodes. A repeat mantoux test showed an induration of 22× ×25 mm. Her total and differential blood counts, tests for serum creatinine, serum calcium, serum angiotensin converting enzyme and serological tests to detect human immunodeficiency virus (HIV) infection were normal.

A 18 FDG-PET scan revealed several metabolically active, bilateral level 5 lymph nodes in the neck, the largest on the left side measuring 1.6 ×1.8 cm with SUV max 5.5 and the largest on the right measuring 1.4 cm with a SUV max 5.2. The lungs and mediastinum were clear. Several metabolically inactive nodes were seen bilaterally in the axilla.

She underwent an ultrasound guided biopsy of a right posterior cervical lymph node suggested by the PET/CT scan. The microscopic examination revealed several medium sized epithelioid granulomas with occasional central necrosis suggestive of tuberculosis.

She was started on standard four drug therapy along with topical and periocular corticosteroids. Two months later there was a marked reduction of clinical anterior chamber activity.

Discussion

The clinical pictures were of active chronic or recurrent uveitic disease with vision threatening complications including complicated cataract. These patients were immunocompetent individuals receiving empirical antitubercular or symptomatic immunosuppressive treatment, without a confirmatory etiological diagnosis in either case. We reinvestigated both these patients in order to achieve an etiological diagnosis.

A strongly positive mantoux test prompted a thorough evaluation for evidence of systemic tuberculosis. Conventional techniques of systemic imaging include mainly chest imaging (chest X-rays or chest CT scans), to detect pulmonary or mediastinal disease. Tissue/bacteriological sampling is then done with sputum stains/cultures (if lung field disease is suspected) or thoracoscopy if mediastinal disease is suspected. Sputum and Bronchoalveolar lavage studies are not very sensitive (65%),[2] whereas thoracoscopic biopsies carry a risk of injuries to the great vessels or severe hemorrhaging (0-8%).[3]

We chose to utilize the newer modality of whole body PET/CT scans. These identified metabolically active lymph nodes and tissues in the cervical region in both patients, in addition to the chest cavity in one patient. These peripheral (cervical) areas of inflammation were easier and safer to biopsy than lung tissue and these accurately targeted invasive biopsies returned an adequate yield of disease-involved tissue. Nodes/tissue that were reactive and likely to return noncontributory biopsies were thus not sampled. Conventional chest imaging may not have been able to suggest these biopsy sites for us.

Confirmatory tubercular histopathology permitted appropriate treatment and potentially allowed for better visual and anatomical outcomes. Similarly, PET/CT scans would have permitted an accurate targeting of active sites of disease for biopsy, from the thoracic cavity as well.

A suggestive clinical picture with confirmatory evidence of tuberculosis from a systemic site should permit a high degree of evidence to initiate antitubercular treatment. This may, in some cases, negate the need to conduct invasive studies on aqueous/vitreous fluids that carry a risk of ocular morbidity.

Increasingly, PET/CT scans are used to accurately define the full extent of systemic involvement, yield material for culture and sensitivity studies (to allow an early diagnosis of drug-resistant tuberculosis) or even potentially to monitor the healing process.

PET/CT scans may suggest the sites of safe high-yield biopsies, thus yielding confirmatory histopathology, cultures, or PCR samples.

1. Doycheva D, Deuter C, Hetzel J, Frick JS, Aschoff P, Schuelen E, et al The use of positron emission tomography/CT in the diagnosis of tuberculosis-associated uveitis Br J Ophthalmol. 2011;95:1290–4
2. . World Health Organization. Approaches To Improve Sputum Smear Microscopy For Tuberculosis DiagnosisLast accessed on 2009 Oct 31 Geneva Expert Group Meeting Report Available from: http://www.who.int/tb/laboratory/egmreport_microscopymethods_nov09.pdf
3. Farrow PR, Jones DA, Stanley PJ, Bailey JS, Wales JM, Cookson JB. Thoracic lymphadenopathy in Asians resident in the United Kingdom: Role of mediastinoscopy in initial diagnosis Thorax. 1985;40:121–4

Source of Support: Nil,

Conflict of Interest: None declared.

Keywords:

Ocular; positron emission tomography; tuberculosis

© 2013 Indian Journal of Ophthalmology | Published by Wolters Kluwer – Medknow