31-year-old female, with a history of controlled SLE, presents to your office with a 2 week history of headache, weakness, dizziness, and nausea.  She also reports a new rash on her legs that is non-pruritic.  She denies any recent illnesses, sick contacts, vomiting, abdominal pain, cough, or shortness of breath.  She has been taking hydroxychlorquine for her SLE and has had little complications from this disease.

Vital Signs

BP-131/72, HR-116, RR-15, O2-100%, T-101.2 F

Physical Exam

General – Mild distress

Skin

HEENT

Neck – Supple, no LAD

Pulmonary – CTA without adventitial breath sounds

CV – Tachycardic without M/G/R

Abdomen – S/NT/ND

PV – 2+ throughout

Neurologic – 5/5 strength throughout, 2+ reflexes throughout

Psychiatric – A&Ox3

Laboratory Screening

1. What is the most likely diagnosis?

2. What other laboratory tests can be helpful in making the diagnosis?