## 3 Results  
Descriptive characteristics of the study population are summarized in Table 1. A total of 66 patients were collected, 45 (68.2%) were female (M:F ratio 0.47, 21/45) with an age at flare of 58.1 \(\pm\) 14.9 years, ranging from 14 to 91; the mean BMI was 26.3 \(\pm\) 4.4 kg/m\({}^{2}\); and 15 (22.7%) were current smokers. A total of 39 (59.1%) had personal history of chronic plaque psoriasis and 17 (25.8%) had a positive family history of psoriasis. Disease age of onset did not differ between patients with history of plaque psoriasis vs. those without. The CCI was 2.2 \(\pm\) 1.9, being arterial hypertension, dyslipidemia, and psoriatic arthritis, the more frequent comorbidities affecting 28 (42.4%), 18 (27.3%), and 12 (18.2%) of patients, respectively. In particular, peripheral arthritis and dactylitis were found in 9 (13.6%) and 3 (4.5%) patients, respectively. Regarding disease course, most of the patients (52 out of 66, 78.8%) had history of relapsing GPP course, and in 20 (30.3%) the flare was persistent, lasting more than 3 months. Considering the frequency of flare, 6 out of 66 (9.1%) had more than one single episode per year, and 4 (6.1%) more than two. Of note, comparing disease severity of the patients with frequent flares (i.e., more than 1 flare every 5 years) versus those with rare flares (i.e., less than 1 flare every 5 years), we found that the former had higher GPPASI compared to latter, 37 (23-43) vs. 19 (10-30); Mann-Whitney U Test \(p\) = 0.007. \begin{table}
\begin{tabular}{c c} \hline \hline
**Number of Patients** & **N = 66** \\ \hline Age, mean \(\pm\) SD years & 58.1 \(\pm\) 14.9 \\ Gender, female N (\%) & 45 (68.2) \\ Age of GPP onset, mean \(\pm\) SD years & 49.5 \(\pm\) 14.5 \\ BMI, mean \(\pm\) SD kg/m\({}^{2}\) & 26.3 \(\pm\) 4.4 \\ History of chronic plaque psoriasis & 39 (59.1) \\ Family history of plaque psoriasis & 17 (25.8) \\ History of palmoplantar pustular psoriasis & 24 (36.4) \\ History of acrodermatitis continua of & 8 (12.1) \\ Hallopeau & \\ \hline
**Smoking Habit** & \\ \hline Current & 15 (22.7) \\ Past & 12 (18.2) \\ Never & 39 (59.1) \\ \hline
**History of GPP Course** & \\ \hline Relapsing (\(>\)1 episode lifetime) & 52 (78.8) \\ \(\geq\)1 flare per year & 6 (9.1) \\ \(\geq\)2 flares per year & 4 (6.1) \\ Persistent (\(>\)3 months) & 20 (30.3) \\ \hline
**Comorbidities** & \\ \hline Charlson comorbidity index & 2.2 \(\pm\) 1.9 \\ Arterial hypertension & 28 (42.4) \\ Hyperlipidemiaemia & 18 (27.3) \\ Psoriatic arthritis & 12 (18.2) \\ Peripheral joint & 9 (13.6) \\ Dactylitis & 3 (4.5) \\ Type 2 diabetes mellitus & 10 (15.2) \\ Ischaemic heart disease & 8 (12.1) \\ Hyperuricemia & 4 (6.1) \\ Obesity & 6 (9.1) \\ History of malignancy & 5 (7.6) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of the patients experiencing a flare of generalised pustular psoriasis. Personal history of PPP and ACH were reported in 24 (36.4%) and in 8 (12.1%) patients, respectively. No differences were found in the prevalence of PPP and ACH in patients with a history of plaque psoriasis versus those without. Severity, localization, triggers, and complications of the GPP flare are summarized in Table 2. In particular, the GPPASI was 22.9 \(\pm\) 13.5 (mean \(\pm\) SD), GPPGA was 3.3 \(\pm\) 0.8, and BSA 47.9 \(\pm\) 29.1%. The VAS of itch and pain was 6.2 \(\pm\) 3.3 and 6.2 \(\pm\) 3.0, respectively. The DLQI was 21.0 \(\pm\) 4.9. Of note, at linear regression analysis DLQI correlated with GPPASI score (\(\beta\) = 0.25, \(p\) < 0.001) and VAS pain (\(\beta\) = 0.95, \(p\) < 0.001). A total of 26 (39.4%) patients had fever and 39 (59.1%) leukocytosis. The most common disease localizations were the trunk (95.5%), superior (92.4%) and inferior limbs (84.8%), folds (60.6%), and head-neck area (57.6%). Nail involvement was found in 33.3% of patients, The most common manifestation was leukonychia and onycholysis affecting 40% and 32% of patients, respectively. Geographic tongue was found in 7 (10.6%), and genital area involvement in 32 (48.5%) of patients.