A 68-year-old male presents to the emergency department complaining of severe headache, which has been worsening over the last three weeks, and new onset blurring of his vision. The pain is limited to the right hemicranium, being maximal in the right temple. The patient has jaw claudication, as well as allodynia, around the right temple. Over the last two days, he has developed blurred vision in the right eye which is examined to reveal anterior ischaemic optic neuropathy (AION). The patient has a past medical history of polymyalgia rheumatica, but stopped taking his prescribed medication two months ago due to an improvement in symptoms. Blood tests demonstrate a raised erythrocyte sedimentation rate (ESR).

Which of the following investigations would be most appropriate to confirm the likely diagnosis?

Options:
explanation: A cranial nerve examination may be useful to determine if cranial nerve involvement is present. Oculomotor motor palsy may occur in 2-15% of patients, but other cranial nerves are rarely involved. It would not be diagnostic for GCA.
name: Cranial nerve examination
label: d
answer: no
explanation: A lumbar puncture (LP) can be a useful diagnostic tool to rule out a number of other differentials for the headache and changes in vision e.g. subarachnoid haemorrhage or multiple sclerosis. It would not be of much benefit in a patient with giant cell arteritis, as the LP would likely be normal.
name: Lumbar puncture
label: c
answer: no
explanation: Magnetic resonance angiography may have a role in patients with large vessel involvement with a normal temporal artery biopsy. As this patient has clear symptomatic involvement of his temporal artery, a biopsy would be the most appropriate first-line investigation. If a biopsy was negative, an MRI may then be considered. An MRI scan would also help rule out or identify evidence of other differential diagnoses such as multiple sclerosis, which can present with similar changes to vision.
name: MRI head
label: b
answer: no
explanation: This patient is likely suffering from giant cell arteritis (GCA, also known as temporal arteritis) - a vasculitis affecting medium- and large-sized arteries. It typically occurs in patients over 50 years of age. GCA has a strong association with polymyalgia rheumatica (PMR), with features of PMR present in around 50% of patients, such as this one. GCA requires rapid recognition and treatment to avoid complications such as permanent vision loss. Patients usually present with rapid onset (less than one month) headache with jaw claudication, and a tender, palpable temporal artery.
Vision testing is vital in all patients, as permanent vision loss may develop suddenly. Anterior ischaemic optic neuropathy (AION) accounts for the majority of ocular complications. A temporal artery biopsy is performed to help confirm the diagnosis, which would show skip lesions. However, treatment with high-dose steroids should be commenced as soon as GCA is suspected and takes precedence over the temporal artery biopsy.
A positive temporal artery biopsy can confirm the diagnosis but, due to the presence of skip lesions, an affected segment may be missed in a biopsy and therefore a negative result does not rule out the condition.
name: Temporal artery biopsy
label: a
answer: yes
explanation: A CT head scan may have a role in investigating patients with large vessel involvement with a normal temporal artery biopsy. It would not be the initial diagnostic investigation of choice for this patient. It could be used to help rule out other differential diagnoses for the headache such as stroke or subarachnoid haemorrhage.
name: CT head
label: e
answer: no

Correct answer: a