F-18 FDG PET/CT findings in a case of spinal cord sarcoidosis

18F-FDG PET/CT helps in unmasking the great mimicker: A case of neurosarcoidosis with isolated involvement of the spinal cord

A 36 year-old male with no significant past medical history presented with lower extremity numbness, gait instability, and urinary and bowel retention of 4 weeks onset. Spine MRI revealed diffuse oedema of cervicothoracic spinal cord with several solid enhancing intramedullary lesions, suggestive of metastases. The ¹⁸F-FDG PET/CT performed to identify the primary malignancy demonstrated mild hypermetabolic foci within the cervicothoracic cord, as well as a mildly hypermetabolic bilateral hilar lymphadenopathy and a mildly hypermetabolic pulmonary nodule, suggestive of sarcoidosis versus metastasis. The diagnosis of sarcoidosis was supported by identifying non-caseating granuloma in the biopsy of the pulmonary nodule. The patient responded well to steroid-therapy, with the symptoms being resolved within 3 weeks.

Fluorothymidine PET/CT in neurolymphomatosis

Neurolymphomatosis, a rare extranodal lymphoma, may involve the cranial nerves, peripheral nerves, spinal nerve roots, or nerve plexus. F-FDG PET/CT however shows increased FDG uptake in the nerves but is not specific for malignancy. We report a patient with neurolymphomatosis who underwent F-FDG PET/CT and F-fluorothymidine PET/CT where both the scans showed increased tracer uptake in the right sciatic nerve, proven later as neurolymphomatosis on nerve biopsy. Furthermore, the F-FDG avid mediastinal lymph nodes did not show F-fluorothymidine avidity, suggesting an inflammatory etiology.

Overview of neurosarcoidosis: recent advances

Sarcoidosis (SA) is a granulomatous, multisystem disease of unknown etiology. Most often the disease affects lungs and mediastinal lymph nodes, but it may occur in other organs. Neurosarcoidosis (NS) more commonly occurs with other sarcoidosis forms, in 1 % of cases it involves only nervous system. Symptomatic NS occurs but on autopsy study up to 25 % of cases are confirmed. NS can affect central nervous system: the brain, spinal cord and peripheral nerves, and muscles. The diagnosis of neurosarcoidosis facilitates diagnostic criteria: histopathological, imaging and cerebrospinal fluid examination, and clinical symptoms. At present, there are no set standards for treatment of patients suffering from NS. Early therapy of symptomatic patients is recommended. Corticosteroids still are the first line of treatment for NS patients. In cases of steroids resistance, lack of their effectiveness or existence of contraindication to their use, immunosuppressant treatment is recommended. The latest NS algorithm with immunosuppressive treatment is discussed.

FDG PET imaging in sarcoidosis

The objective of this review is to highlight the clinical utility of FDG-PET/CT for evaluation of patients with chronic sarcoidosis. The emphasis was on the potential advantages and disadvantages of this technique in these patients based on which recommendations were made. The advantage of FDG-PET/CT technique is that it can visualize FDG accumulation in activated inflammatory cells and simultaneously provide PET and CT images. Of particular interest is the use of FDG-PET/CT for the staging and identification of occult sites and sites suitable for biopsy and for the assessment of inflammatory active sarcoidosis in patients with prolonged symptoms, especially when other markers of the disease are within normal values. FDG-PET/CT also provides a better visualization of extrathoracic sites of active sarcoidosis, such as in the bones, liver, spleen, and retroperitoneal lymph nodes. The use of FDG-PET/CT is of special interest in cardiac sarcoidosis because this potentially life-threatening disease is sometimes present in asymptomatic patients. FDG-PET/CT also has a role in the clinical management of patients with chronic persistent sarcoidosis, such as for planning treatment, monitoring response, and long-term follow-up. The limitations of FDG-PET/CT in patients with sarcoidosis are discussed in the context of a "sarcoidosis-lymphoma syndrome" and potentially excessive radiation exposure. Further prospective multicentre studies are needed to refine the clinical applications of FDG-PET/CT in patients with sarcoidosis and drive the field forward.

The scar sign: a useful finding on FDG PET/CT to distinguish sarcoidosis from other causes of lymphadenopathy

Scar involvement is a rare but characteristic cutaneous manifestation of sarcoidosis. The concurrent presence of FDG-avid lymphadenopathy and scar involvement (the "scar sign") is a useful finding on FDG PET/CT to suggest sarcoidosis, especially when biopsy specimens are difficult to obtain. A 46-year-old woman who presented with fever, cough, and weight loss was found to have mediastinal and hilar lymphadenopathy on chest radiography and CT scan. FDG PET/CT scan showed FDG-avid lower cervical, mediastinal, hilar, and inguinal lymphadenopathy. There was also increased FDG uptake along an old hysterectomy scar. Mediastinoscopy and nodal biopsy revealed noncaseating granulomas compatible with sarcoidosis.

Findings of multiple neuritis on FDG PET/CT imaging

A 56-year-old woman with weight loss, facial pain, and weakness underwent FDG PET/CT to detect a tumor of unknown origin. The images did not detect any lesion typical of malignancy. However, elevated FDG activity in several cranial and peripheral nerves was noted and suggestive of multiple neuritis. Following therapy for neuritis, the patient's symptoms improved.