Table 1

Association of all lesion characteristics with asymptomatic PML lesions

Lesion characteristicsTimes rated in PML lesions*
Times rated in MS lesions*
OR for PML†95% CIp Value‡
General characteristics
 Bilateral hemispheric involvement§41620.500.15 to 1.60.24
 Unilobar lesion dissemination¶41292.30.74 to 7.50.30
 Multilobar lesion dissemination¶23132.90.57 to 15.10.30
 Widespread lesion dissemination4168reference
 Mass effect10NANANA**
 Signs of oedema120.50.041 to 6.60.62
 Lesion size >3 cm††330NANA<0.001‡‡
Lesion location
 Frontal lobe49401.50.54 to 4.30.42
 Parietal lobe13210.600.20 to 1.80.35
 Occipital lobe1033.80.78 to 18.10.099
 Temporal lobe6100.610.17 to 2.10.44
 Corpus callosum05NANA0.060§§
 Basal ganglia4100.400.077 to 2.00.27
 Brainstem12150.820.21 to 3.30.77
 Cerebellum1854.30.89 to 21.30.070
Tissue involvement
 Juxtacortical WM63323.61.2 to 11.10.023
 Deep WM47530.820.36 to 1.90.64
 Periventricular WM1270.0280.0036 to 0.220.001
 Cortical GM23214.83.6 to 61.1<0.001
 Deep GM1381.80.38 to 8.10.47
Lesion appearance
 Focal lesion appearance¶¶471070.0260.0081 to 0.083<0.001
Lesion bordersn=103n=108
 Ill-defined border towards WM***45139.14.0 to 20.5<0.001
 Mixed border towards WM***26116.21.9 to 20.5<0.001
 Sharp border towards WM3284reference
 Ill-defined border towards GM***20103.71.6 to 8.80.001
 Mixed border towards GM***36144.81.6 to 14.50.001
 Sharp border towards GM4278reference
Specific PML characteristics
 Presence of punctate T2 lesions†††561135.618.9 to 974.7<0.001
MRI sequences and contrast enhancement
 T1 hypointense‡‡‡31 (n=74)47 (n=71)0.370.11 to 1.20.107
 T2 hyperintense‡‡‡110 (n=110)92 (n=93)NANANA
 FLAIR hyperintense‡‡‡105 (n=108)102 (n=103)2.90.25 to 34.50.397
 Presence of contrast enhancement23 (n=92)2 (n=59)9.51.1 to 82.20.041
  • Bold values are statistically significant.

  • *Rated by four readers in 41 patients (21 with PML lesion(s) and 20 with new MS lesion(s)).

  • †OR>1 is associated with PML lesions, OR<1 is associated with new MS lesions.

  • ‡For test of model effects.

  • §Compared to ‘unilateral hemispheric involvement’.

  • ¶Compared to ‘widespread lesion dissemination’.

  • **Mass effect was rated as present once, resulting in complete data separation.

  • ††Compared to ‘lesion size <3 cm’.

  • ‡‡Calculated by Pearson χ2.

  • §§Calculated by Fisher's exact test because of complete data separation (ie, in either the PML or the MS lesion group the characteristic is either present or absent for all cases), and thereby ignoring the repeated scorings within a patient.

  • ¶¶Compared to ‘non-focal appearance’ (ie, rated as: diffuse, confluent irregular or infiltrative appearance).

  • ***Compared to ‘sharp borders’.

  • †††Defined as punctiform T2/FLAIR hyperintense lesions in the vicinity of the main PML lesions recently described as ‘milky way appearance’ and/or punctiform T2/FLAIR hyperintense lesions with a perivascular spread (<5 mm in diameter).

  • ‡‡‡Compared to isointense/not visible on this sequence.

  • FLAIR, fluid-attenuated inversion recovery; GM, grey matter; MS, multiple sclerosis; NA, not applicable; PML, progressive multifocal leukoencephalopathy; WM, white matter.