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Copyright ©ERS Journals Ltd 2008
Finger clubbing and altered carbon monoxide transfer capacity in cannabis smokers
1 Dept of Respiratory Diseases, Reference Center for Orphan Lung Disorders, Louis Pradel Hospital, Hospices Civils de Lyon, Lyon I University, 2 Dept of Internal Medicine, Edouard Herriot Hospital, Hospices Civils de Lyon, Lyon, France.
To the Editors:
The harmful effects of cannabis smoking on the lung include: an increased risk of airway obstruction 1 and, presumably, of lung cancer; large cystic and bullous changes 2; pneumothorax; and pneumomediastinum. Here we report on two patients with finger clubbing and hypoxaemia, probably related to long-term smoking of cannabis, in the absence of any overt disease.
The first patient, a 26-yr-old male, presented with chronic dyspnoea on exertion. He had 10 pack-yrs of tobacco smoking and had smoked 15 cannabis cigarettes per day for 10 yrs. Examination was unremarkable except for marked digital clubbing of the hands and feet. Pulmonary function tests (PFTs) were within normal limits (table 1
), except for decreased carbon monoxide (CO) lung transfer capacity and hypoxaemia at exercise. A computed tomography (CT) scan of the chest was normal, and alveolar–arterial oxygen tension difference (PA–a,O2), while breathing 100% oxygen was normal.
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The patient quit tobacco smoking and persistently reduced cannabis use to one cannabis cigarette per month. One year later, dyspnoea had resolved and finger clubbing had almost disappeared. Spirometry was normal. The transfer factor and the transfer coefficient of the lung for CO (KCO) had both increased to 73 and 67% of the predicted, respectively. Arterial oxygen tension at rest was 9.5 kPa (supine) and 11.2 kPa (upright), and 10.2 kPa at exercise (10 min at 50 W); PA–a,O2 was elevated in the supine position (27 kPa) and normal while standing (14 kPa). Contrast echocardiography was normal in supine and upright positions.
The second patient, a 27-yr-old male, was referred for marked finger clubbing and chronic dyspnoea at exercise. He had smoked 20 cigarettes of tobacco and 
10 cigarettes of cannabis per day for 8 yrs. PFTs demonstrated normal volumes but there was decreased CO transfer and hypoxaemia at rest. A CT scan of the chest showed mild paraseptal emphysema.
18-F-fluoro-2-deoxyglucose-positron emission tomography, radionuclide lung scanning, echocardiography and routine blood tests were normal in both patients.
Finger clubbing in our patients could not be related to any known cause or family history despite thorough evaluation, and was eventually considered to be related to heavy cannabis use, with 150 and 80 cannabis cigarette-yrs, respectively (i.e. daily number of cannabis cigarettes x number of yrs smoked). The previously unreported regression of the finger clubbing upon reduction of cannabis smoking confirmed its responsibility (although the patient also quit tobacco smoking), as previously suspected 3. In addition, both cases presented with severe hypoxaemia at exercise and alteration of CO transfer capacity, despite the lack of significant emphysematous changes on chest imaging and the absence of any obstructive defect at spirometry. These observations contrast with the reported lack of effect of cannabis on KCO 1.
The pathophysiology of cannabis-induced finger clubbing remains speculative. We hypothesise that the drug may increase the expression of vascular endothelial growth factor-
or of its receptor 4. Cannabis-induced alteration of carbon monoxide transfer may be related to vascular changes and/or infiltration by pigmented macrophages of the alveolar interstitium and capillaries of the lung, as shown by autopsy analysis of cannabis smokers (also showing bronchiolar inflammation) 5.
Statement of interest
None declared.
REFERENCES
- Aldington S, Williams M, Nowitz M, et al. The effects of cannabis on pulmonary structure, function and symptoms. Thorax 2007; 62: 1058–1063
- Johnson MK, Smith RP, Morrison D, et al. Large lung bullae in marijuana smokers. Thorax 2000;55:340–342.
[Abstract/Free Full Text] - Baris YI, Tan E, Kalyoncu F, et al. Digital clubbing in hashish addicts. Chest 1990;98:1545–1546.
- Atkinson S, Fox SB. Vascular endothelial growth factor (VEGF)-A and platelet-derived growth factor (PDGF) play a central role in the pathogenesis of digital clubbing. J Pathol 2004;203:721–728.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
- Morris RR. Human pulmonary histopathological changes from marijuana smoking. J Forensic Sci 1985;30:345–349.[Web of Science][Medline] [Order article via Infotrieve]
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