1. Check they actually are chilblains. Raynaud’s syndrome is often misreported as chilblains, so take a history. The diabetic foot, or PVD, can also be misreported/misdiagnosed as chilblains. Check peripheral pulses.
2. This is, apparently, and with all due apologies to Dr House, a situation where it is sometimes lupus. Chilblains persisting/commencing in the summer months can be a sign of SLE or other connective tissue diseases. So, ask about all those other symptoms of connective tissue diseases that I can never remember – rash and arthralgia/arthritis (which I did remember), photosensitivity (which I should have but didn’t), and oral ulcers, seizures, and psychotic symptoms (which I’d never have thought to link to CT disease). If suspicious, check ANA – other tests are not usually helpful.
3. Treatment. There is not a huge amount of evidence available on best treatment, but, based on one extremely small RCT, 60 mg Nifedipine daily seems to be of benefit. I’d never heard of Vitamin D as a treatment, but apparently it doesn’t work anyway so that doesn’t matter.