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Diagnosis of acute sinus infections
There are times when papers are so good that one wants to jump for joy, or weep because one hasn't done it oneself. Bandolier felt this way about a beautiful demonstration of how to sort out diagnosis, in this case diagnosis of acute sinus infections in primary care [1].

Study

It was a prospective study of 357 patients intended to examine a range of symptoms and signs, and simple blood tests against computed tomography in the diagnosis of acute sinus infection. Some people couldn't be included (pregnant women, for example), some didn't want a scan, and pressure on scan time meant that not all could be scanned. Information was therefore available on 201 people.

They had all received a diagnosis of acute sinus infection and were considered to be in need of antibiotic therapy. A host of symptoms and signs were recorded, and within two days of the clinical diagnosis they had a CT scan which included the entire nasal cavity and the paranasal sinuses. The scans were interpreted independently by two radiologists, with re-evaluation and consensus in case of disagreement. Sinusitis was defined as total opacification or fluid level in an ethmoid, sphenoid, frontal or maxillary sinus.

Altogether 17 symptoms and 10 signs were examined, together with results of ESR, C-reactive protein and white blood counts.

Results

In the 201 patients who underwent a CT scan, 127 (63%) had acute sinus infection diagnosed by the CT scan. When the signs, symptoms and blood tests were subjected to logistic regression analysis, it was found that only four were significantly associated with presence of infection. They were:

  1. Purulent secretion in cavum nasi
  2. Purulent rhinorrhoea
  3. Double sickening
  4. ESR >10 mm/hr
"Double sickening" was defined as the presence of two phases in the illness history .

The likelihood ratios calculated for the presence of 0, 1, 2, 3 or 4 of these signs and symptoms in 199 of the 201 patients are shown in the Table.
Diagnosing acute sinusitis
Number of signs and symptoms Sinusitis present Sinusitis absent Likelihood ratio
4 43 1 25.2
3 41 13 1.8
2 32 23 0.8
1 8 22 0.2
0 2 14 0.1
Total 126 73 ---

Comment

The implication of these findings are that acute sinusitis is over-diagnosed in primary care (though that has been shown before). For Norwegian GPs, a putative diagnosis of acute sinusitis is likely to be correct 63% of the time. If a patient has the four relevant signs and symptoms, that post-test probability increases to over 95%, with 3 of the four to about 80%. But if there are none, there is only a 15% chance that the patient has sinusitis.

Can this be applied generally? There is no obvious reason why not (Norwegian GPs usually have ESR and other testing available on site). In any event, this award-winning paper shows "how to do it" in sinusitis and in any other area. A pleasure and privilege to read, and a "must have" for anyone seriously interested in making evidence count in diagnosis.

References:

  1. M Lindboek, P Hjortdahl, U Johnsen. Use of symptoms, signs, and blood tests to diagnose acute sinus infections in primary care: comparison with computed tomography. Family Practice 1996 28: 183-8.



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