SFN and pachyonychia congenita: Most of the PC patients (6 out of the 8 (75%) SFN+ patients and 5 out of the 10 (50%) SFN− patients) experienced a paucisymptomatic disease (WHO clinical progression scale 2); only two patients (1 out of the 8 (12.5%) SFN+ patients and 1 out of the 10 (10%) SFN− patients) categorized as WHO clinical progression scale 5 were hospitalized and treated with low flow oxygen therapy.