Systemic lupus erythematosus

For MRCP PACES candidates,
besides Psoriasis, please remember this as one of the most common exam questions.
I got this case in my 3rd attempt of PACES in Malaysia.

This patient has a malar rash. Describes as erythematous rash over the cheeks and bridge of nose and sparing the nasolabial folds. There is also presence of hypo and hyperpigmentation, however there is no follicular plugging.
My diagnosis is that this patient most likely has SLE and I would proceed to look for oral ulcers, discoid lupus, arthritis, alopecia, listen to the heart for pericardial rub, listen to the lungs for pleural effusion(serositis) and examine the abdomen for presence of hepatosplenomegaly. I would also like to look at the fundus for cytoid bodies.

Criteria for SLE
1) Malar rash
2) Discoid lupus
3) Photosensitivity
4) Oral ulcers
5) Arthritis
6) Serositis (Pleuritis/Pericarditis)
7) Renal disorder : Proteinuria >500 mg/d or cellular casts
8) Neurological disorder
9) Haematological disorder
10) Immunological disorder : anti dsDNA, anti Smith Ab, ACA/LA, false positive VDRL
11) ANA

Need 4 out of 11 criteria

What investigations would you perform to look for activity ?
ESR, C3, C4, CRP

What is the most common neurological manifestation ?
Psychosis