Solitary fibrous tumour of the pleura: a rare cause of digital clubbing

Background

Digital clubbing is a uniform deformity of the distal phalanx soft tissue resulting in loss of the normal angle between the nail and nail-bed. When identified, a thorough history, examination and investigation for a cause should be sought, as the sign is associated with a serious underlying condition in 40% of cases.1

Paraneoplastic syndromes secondary to solitary fibrous tumours of the pleura (STFP) are a well-documented association, the most common being Pierre-Marie-Bamberger—a triad of finger clubbing, hypertrophic osteoarthropathy (HPOA) and arthralgias.

Although rare, case reports suggest between 20% and 35% incidence of Pierre-Marie-Bamberger syndrome in patients with SFTP.2 3 The exact mechanism of finger clubbing in these patients is not known but thought to be due to excessive secretion of hyaluronic acid from the tumour and abnormal synthesis of hepatocyte growth factors.4

Another presentation of SFTP is Doege-Potter syndrome which has been described in approximately 4% of STFPs. This is characterised by hypoinsulinaemic hypoglycaemia due to the release of insulin like growth factor from the tumour which activates insulin receptors, increasing uptake of peripheral glucose.5

SFTPs are generally benign but do rarely show malignant transformation. It is a slow growing tumour and therefore can be asymptomatic on presentation. Factors that may indicate malignancy include high cellularity and mitotic activity, haemorrhage and necrosis.6

Case presentation

A woman in her early 70s presented to fracture clinic after sustaining a wrist fracture. She was noted by the orthopaedic registrar to have finger clubbing (figure 1) and referred back to the GP for further investigation.

She was promptly assessed by her GP and was referred for a chest X-ray on the same day. Her X-ray was highlighted as abnormal by the performing radiographer and the patient had a CT chest and abdomen with contrast on the same day.

She was discharged home and an outpatient respiratory referral with multidisciplinary team meeting (MDM) discussion was organised.

A biopsy of the mass was organised 4 weeks after initial referral.

On outpatient respiratory review, the patient reported a year long history of shortness of breath when walking on an incline but unlimited flat exercise tolerance. She did not describe any chest pain, cough or haemoptysis, and had no significant weight loss. She had a five pack-year history but had not smoked for over 50 years.

On examination the patient was found to be well with finger clubbing and reduced breath sounds on the left on auscultation. Her preassessment lung function tests suggested a saturation of 96% with an FEV1 at 64% of her predicted (FEV1 1.04, FVC 1.43, TLCO 4.38, KCO 1.94).

Her surgery took place 10 weeks after initial referral at a specialist centre.

Investigations

A chest radiograph was performed which identified a large left thoracic mass with a pleural effusion (figure 2). A subsequent CT thorax was arranged which demonstrated a well-defined, mildly heterogeneous, 20×12 cm mass, occupying almost the entire left hemithorax (figure 2). There was no destruction of the overlying ribs. Imaging findings were consistent with a pleural-based mass given the large size, the mass forming an obtuse angle with the chest wall and compressive atelectasis of the underlying lung.

A CT-guided biopsy was performed and the histopathology was in keeping with likely SFTP. The patient was referred to a quaternary thoracic surgery referral centre to be discussed at a specialist MDM. Her tumour was resected without complications and the final surgical histology confirmed SFTP with atypical features (figure 2). She recovered well postoperatively and remains under clinical follow-up.

Generally patients will receive 5 years of follow-up with clinical examination and CT thorax at 3–6 monthly intervals.

Differential diagnosis

A potential differential would be a lung parenchymal mass.The mass in this case formed an obtuse angle with the chest wall with compressive atelectasis of the underlying lung in keeping with a pleural-based lesion.

The differential for pleural-based masses are generally malignant causes and include a localised mesotheolioma, pleural lymphoma or pleural metastases. These would usually present with significant respiratory symptoms and other features of malignancy on imaging such as a large pleural effusion, thoracic lymphadenopathy, rib destruction or distant metastases.

The last differential would be SFTP—a large, well-defined, pleuralbased mass with no evidence of metastasis, as was in the case above.

Treatment

Surgery—thoracotomy with removal of tumour is thought to be curative.

A small minority of patients may receive chemotherapy or radiotherapy.

Outcome and follow-up

On follow-up, the patient reports marked improvement infinger clubbing at 6 months postoperatively.

Follow-up varies from centre to centre, several larger centres in the UK follow-up with CT imaging for 5 years, although 23% of recurrences occur outside of this timeframe, so a low threshold for reimaging patients beyond 5 years should be adopted.7

Tumours larger than 10 cm are associated with a higher malignacy potential. Similarly, patients who have received an incomplete resection should be followed with a higher index of suspicion for recurrence.