Utility of the white blood cell scan in a case of pyrexia of unknown origin

Clinical History

69-year-old gentleman presented with diabetic ketoacidosis which responded to intensive fluid resuscitation and insulin but was complicated with pyrexia and rising inflammatory markers. Initial investigations suggested a source of infection. He was treated with courses of antibiotics, but his pyrexia failed to settle, and further imaging was required.

Imaging Findings

The patient’s X-rays, abdominal ultrasound and echocardiogram were negative. A CT chest-abdomen-pelvis (Fig. 1) showed a patchy altered enhancement pattern in the various parts of both kidneys consistent with pyelonephritis, and blood cultures revealed gram-negative bacilli.

He was treated with IV tazocin and gentamicin. However, despite being on antibiotics for three weeks, he remained pyrexic with a CRP of >200. He was having pyrexia of unknown origin (PUO) despite investigations and treatments.

To screen for potential sources of PUO, a whole body white blood cell (WBC) scan was requested. (Fig. 2) ¹¹¹in-labelled white cell scan with hybrid SPECT/CT (Fig. 3, 4) demonstrated very high white cell accumulation throughout the dilated left femoral vein suggesting deep vein thrombosis (DVT) or thrombophlebitis, and low molecular weight heparin was started. Leg Doppler USS the following day confirmed the left femoral DVT, and warfarin was added.

The patient recovered uneventfully after that.

Discussion

Pyrexia of unknown origin, or PUO, is one of the classic clinical conundrums in modern medicine, with one of the widest ranges of differential diagnoses. It was initially defined by Petersdorf and Beeson in 1961 and later modified to include the criteria: a temperature greater than 38.3°C, lasting for at least 3 weeks and failure to reach a diagnosis after 3 days of inpatient investigation or after 3 or more outpatient visits. [1] There are various causes of PUO including infections (15-30%), neoplasms (10-30%), connective tissue disorders (33-40%) and a category labelled ‘miscellaneous’ (5-14%), which groups together a number of rarer conditions, including DVT, which are recognised as a cause for PUO. [1]

Initial assessment of PUO includes thorough history and examination, and laboratory and radiological tests such as CXR, USS and CT (chest, abdomen, pelvis). [1]

WBC scintigraphy identifies whole body WBC distribution and can locate a potential site of infection/inflammation in patients with PUO. [2] The sites of abnormal WBC accumulation and associated morphological abnormalities, e.g. abscess, graft infection etc. can be visualised better with the additional hybrid SPECT/CT in the same session. WBC scintigraphy may be used in PUO especially when other imaging tests are uninformative or contraindicated. [3, 4]

DVT may sometimes present without any of the classical symptoms such as leg pain, swelling and inflammation, and is more common in the elderly population. It can progress to pulmonary embolism (PE) which can be fatal in case of major PE if not picked up early. [5] It demands a high index of suspicion especially in elderly patients with known risk factors. [6]

This case highlights the limitations of clinical assessments and routine investigations in PUO, an atypical presentation of DVT, and the benefit of whole body ¹¹¹in-labelled WBC scan with SPECT/CT in the diagnosis and the management of PUO.

Differential Diagnosis List

Final Diagnosis

Deep venous thrombosis in the left femoral vein causing PUO

URL:	https://www.eurorad.org/case/12790
DOI:	10.1594/EURORAD/CASE.12790
ISSN:	1563-4086