A patient presents with painless unilateral vision loss. You diagnose her with anterior
ischemic optic neuropathy (AION). Upon further questioning, you discover that she does not have
a headache or any scalp tenderness, and shows no signs of weight loss or joint soreness. However,
she mentions that she experienced one to two minutes of vision loss approximately six weeks ago.
So, what do you do?
First, order lab tests to either rule out or confirm a diagnosis of giant cell arteritis (GCA). The two key
tests you must order include:
- ESR (erythrocyte sedimentation rate).
- C-reactive protein.
Make sure you write "STAT" on the testing instructions, because the faster you obtain the information,
the sooner you can begin treating a patient who may be experiencing a
medical emergency.
An individual's normal ESR varies by both age and gender. For men, an elevated ESR is defined as any measurement
that is greater than the patient's age, divided by two (age/2). For women, however, an elevated ESR is defined
as any measurement that is greater than the patient's age, plus 10, divided by two ((age+10)/2). An elevated ESR
indicates increased overall inflammation, but is not specific.
Unlike ESR, C-reactive protein testing is specific for
artery inflammation and can be used to help with the
diagnosis of GCA. However, C-reactive protein results take longer to obtain than ESR results. And, in almost
any case of AION, an elevated ESR alone is sufficient to refer the patient to a neurologist for a confirmatory
temporal artery biopsy, as well as to initiate therapy for GCA (typically high doses of oral steroids).
Keep in mind: While both ESR and C-reactive protein can serve as invaluable tests, if a patient presents with
any symptoms directly indicative of GCA, immediately refer him or her to a neurologist or neuro-ophthalmologist.
At the end of the day, only a temporal artery biopsy can decisively confirm GCA.
