REF011 - DaTSCAN Imaging

The purpose of this document is to assist clinicians in deciding on the appropriateness of a Nuclear Medicine DaTSCAN investigation and to give guidance on the mechanism of referral.

Distinguishing Parkinson’s disease from Essential Tremor, Lewy Body Dementia and other forms of dementia, including Alzheimer’s disease is not straightforward. A variety of investigations, including neuro-imaging assessments assist in the process but the diagnosis frequently remains unclear. This has resulted in patients with Parkinson’s disease and Lewy Body Dementia being exposed to inappropriate treatments with significant side effects and to delays in the commencement of more appropriate treatment.

In older patients, the diagnosis of Parkinson’s disease is complicated further by ageing effects. In particular, slowing of gait and movement is common, as are tremors. These symptoms may mimic Parkinson’s disease in patients without the condition.

Iodine-123 labelled Ioflupane marketed under the trade name DaTSCAN is a ligand that binds to dopamine transporter proteins on presynaptic nerve terminals.

In Essential Tremor, the binding is good and uptake in the neurons is good. In Parkinson’s Disease, loss of dopamine neurons causes a reduced uptake of the radiopharmaceutical giving a different pattern of uptake in the caudate and putamen of the dorsal striatum that allows differentiation to be made.

• The referrer may be a clinician holding a current valid medical qualification and currently employed in secondary care as a Neurologist, Geriatrician or Psychiatrist.

Referring clinicians are reminded of the requirement to avoid unnecessary exposure to ionising radiation. The investigation may already have been requested at this hospital or elsewhere and clinicians are asked to be particularly vigilant to ensure that their request is not a double request.

Requests will only be accepted if the diagnostic question fulfils one of the referral criteria detailed in the following paragraph. Appropriate clinical information must be supplied to allow the investigation to be justified. Requests will be returned to the referrer if:

• The diagnostic question is unclear.
• The diagnostic question cannot be answered by the investigation.
• Insufficient clinical information is supplied to justify the investigation.

Requests should be submitted on the orange stripe NUCLEAR MEDICINE (ISOTOPE SCAN) request form. Patient details, investigation required and reason for test/diagnostic question should be fully and appropriately completed. The form MUST be signed.

Sufficient clinical information must be provided to justify the investigation proceeding.

The clinical indications are detailed below.

NB Diagnosis of Lewy body Dementia cannot be made by a DaTSCAN in patients with pre-existing Parkinson’s Disease.

To decrease thyroid accumulation of radioactive Iodine-123, the patient's thyroid gland must be blocked by a thyroid-blocking agent at least one hour before administration of the DaTscan.

• Thyroid Blockade: Typically 130mg potassium iodide tablets (usually 2 x 65mg tablets, equivalent to a total of 100mg of iodide) to be taken at least 1 hour before the injection.
• If potassium iodide is unavailable, potassium iodide should NOT be prescribed; alternatives such as Lugol's solution can be used (0.8ml contains 104mg of iodide) - can be given with milk or water/cordial.
• If patient is allergic to iodine, potassium iodide or Lugol's solution must NOT be given. The ARSAC licence holder should be consulted. In this circumstance, an alternative thyroid blocking agent may be used.
• See the ARSAC Notes for Guidance (section 8) for further details and alternatives^[1].
• Patients do not need to stop any medications prior to DaTSCAN (based on discussions with Prof Avery & Southampton University Hospitals) but should bring with them a list of their current medications.
• A wide variety of drugs interact with the radiopharmaceutical uptake and may cause misleading results. Some of the drugs may remain active for a long time after withdrawal so it is necessary to check current and recent medication that the patient may have stopped. A full list of current and recent past medication should be recorded. This must be forwarded with the referral card for use at reporting.

• Remove hearing aids, ear-rings, hair clips etc.