Discussion
Hernandez-Rodriguez et al. described and validated 4 main histological patterns among TAB from GCA patients. Patterns of inflammation were defined according to the extent and distribution of inflammatory infiltrates through the artery wall as follows :
  1. Adventitial pattern  : presence of inflammatory cells only in the adventicia and preservation of media and intima layers (5.6%) ;
  2. Advential invasive pattern  : adventitial infiltration followed by local invasion of the muscular layer with integrity of the intima (7.3%) ;
  3. Concentric bilayer pattern  : inflammatory cells infiltrate the adventitia and the intima with preservation of the media (18.2%) ;
  4. Panarteritic pattern  : inflammatory infiltrates are distributed through the 3 arterial layers (68.8%).
They also proposed a scoring system according to the severity of the vessel invasion : « mild infiltrative pattern » including adventitial pattern and adventitial invasive pattern, scored as 1 and 2 ; and « extensive infiltrative pattern » including concentric bilayer pattern and panarteritic pattern, scored as 3 and 4 (Figure 3 ) (5).
Figure 3. Histological Patterns involving the Temporal Artery in GCA and scoring system according to Hernandez-Rodriguez et al.
Another important point of Hernandez-Rodriguez et al. is the proposition of a dynamic model of arterial inflammation in GCA based on the fact that different histological patterns are observed in TAB from GCA patients and that those different inflammatory patterns may coexist in a same artery with the presence of normal and/or healing sections (Figure 4 ) (5).
Figure 4. Dynamic model of arterial invasion adapted from Hernandez-Rodriguez et al.
Besides the 4 histological patterns, the scoring system and the proposal of a dynamic model of arterial invasion, Hernandez-Rodriguez et al did not find clear correlation between the different patterns and clinical or biological findings at disease diagnosis although abnormalities on temporal artery palpation and some cranial symptoms seems to occur mostly in patients with panarteritic pattern on TAB (5).
The main clinical features in this patient were the deterioration in the general status and visual blurring. Permanent visual loss is the most severe complication of GCA and is often an early manifestation of the disease (7). Chatelain et al found that the presence of giant cells on TAB was associated with permanent vision loss and also found a positive correlation between the quantity of giant cells and the risk of blindness. However, they found no association between the abundance  of the inflammatory infiltrate, and the presence of arterial thrombosis (7). Makkuni et al showed that the degree of intimal hyperplasia on TAB seems to be closely associated with neuro-ophtalmic complications of GCA (8). Hernandez-Rodriguez et al showed that the presence or absence of giant cells and the extent of intimal hyperplasia did not correlate with cranial and neuro-ophtalmic ischemic manifestations (5).
The young age of our patient has contributed to the relative delay of GCA diagnosis, making it less likely. Indeed, GCA is well described in patients of 50 years and older with incidence of the disease increasing with age (9,10) making the diagnosis here more challenging.