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How is Niemann-Pick type C disease diagnosed?

Niemann-Pick type C disease (NP-C) is difficult to diagnose because the symptoms can occur at different times and with varying severity in each person. For some patients, symptoms are quickly linked to NP-C by their doctor, but for others, it may take many different doctors a number of years to finally link them together and suspect NP-C. Table 1 below shows common tests that doctors may recommend in order to help reach a diagnosis. If a doctor suspects that some of the symptoms experienced could be due to NP-C, confirmatory tests may include:1

  • A skin biopsy to obtain tissue cells that are then cultured for several weeks and observed under a microscope to see whether there is accumulation of fatty molecules within a cell
  • A blood sample to test DNA for affected genes (mutations) that cause NP-C.

Table 1: Understanding other common tests doctors might suggest

Name of test What it involves
Ultrasound2 (or Sonogram) A scan that uses high-frequency sound waves to look at organs and structures inside the body. During an ultrasound scan, the technician or doctor moves a device called a transducer over part of the body. The transducer sends out sound waves and the waves bounce off the tissues inside the body and return to the transducer, which uses the returning waves to create images. In NP-C, the ultrasound is used to detect an enlarged liver or spleen.1
 
Biopsy3 A procedure in which the doctor removes a small amount of tissue for examination in a laboratory. Biopsies help doctors to diagnose or rule out a condition and different biopsy techniques are used depending on which tissue or organ needs to be studied. Skin biopsy is an important diagnostic test for NP-C. It involves removal of a small cylindrical piece of skin using a special device that punches a small hole through the layers of the skin. This is often made with local skin anesthetic. Filipin testing is then performed on the skin sample to see whether there is accumulation of NP-C specific fatty molecules within the cells. In some cases, for example, in neonatal cases, liver biopsy could be part of the NP-C diagnosis procedure. In a liver biopsy, a needle is guided by ultrasound towards the surface of the liver, where the biopsy is then taken
 
Electroencephalogram (EEG)2 A scan that is used to help understand why the patient is having seizures and if so, what type. An EEG is also used to find the causes of other symptoms such as confusion or sleep problems. The scan is painless, but the patient might find that having electrodes on their skin feels strange. The electrodes record brain activity but do not produce any sensation.
 
Lumbar puncture (or spinal tap)3 A procedure which collects fluid from within the spinal cord (cerebrospinal fluid) to check for the presence of disease or injury. A needle is inserted in the lower spine and positioned in the space between the spinal cord and its covering (this is known as the subarachnoid space). Pressures can then be measured and fluid can be collected for testing.
 
Bone marrow aspiration and biopsy3 A procedure which collects a small amount of bone marrow in liquid form for examination. Bone marrow is the soft tissue found in the hollow part of most bones. The bone marrow is usually removed from the pelvic or breast bone. During the procedure, the skin will be cleaned and a numbing medicine (local anesthetic) applied to the area and surface of the bone. Then, a thick needle with a tube attached is inserted into the bone and the fluid is collected. The needle is then removed. Bone marrow biopsy can be a useful indicator of the extent a patient is affected by NP-C.1
 
Magnetic resonance imaging (MRI)2 A scan that uses magnetic and radio waves to look inside the body. During the scan, the patient lies on a table that slides inside a tunnel-shaped machine. The scan can take a long time and the patient must lie still. The scan is painless but the MRI machine is noisy, so patients usually need to wear earplugs. In NP-C, MRI scans are used to detect changes in the brain.1
 

Due to advancements in diagnostic tests, lumbar punctures and bone marrow biopsies are rarely undertaken to diagnose NP-C. However, these tests may be carried out by a doctor if they think the child is presenting with a different condition. Some of these tests are quite complicated and can only be carried out at specialist laboratories. This means that results may not be available for several weeks. A new plasma oxysterol test may be helpful in confirming diagnosis of NP-C in the near future.1

Many cases of NP-C are either misdiagnosed or go unnoticed. This is because the disease is extremely rare and the symptoms can vary widely between patients.4 Patients may have to see different doctors for different symptoms. For example, a patient would see a psychologist and a neurologist if they experienced psychological symptoms and had trouble with balance, but the two sets of symptoms may not be immediately connected to each other or to NP-C.

 

Providing doctors with the full picture


If you think that you, a family member, or friend may have symptoms suggestive of NP-C, it is important to be persistent in your pursuit of a diagnosis. Early diagnosis can lead to earlier treatment, which can help slow down the rate at which the disease progresses.1 It can also mean that support can be accessed earlier and the right level of help needed is received.

Patient research has shown that persistence has been the key to diagnosis for many patients with NP-C.5 This persistence involves sharing as much information as possible with doctors. Describing all the symptoms to doctors, even when some may seem completely irrelevant, can really help.

If you or a family member is diagnosed with NP-C, you may feel relieved at finally knowing what the cause is but you will also probably be shocked at receiving the news. Some find it helpful to find out as much as they can about NP-C, how it is managed and what support there is in their area, while others prefer to take each day as it comes.

 

References

  1. Patterson MC, Hendriksz CJ, Walterfang M, et al, on behalf of the NP-C Guidelines Working Group. Recommendations for the diagnosis and management of Niemann–Pick disease type C: An update. Mol Genet Metab 2012;106(3):330-344.
  2. MedlinePlus, a service of the U.S. National Library of Medicine and the National Institutes of Health, http://www.nlm.nih.gov/medlineplus/medlineplus.html Last accessed September 2012.
  3. NHS Choices, http://www.nhs.uk/Pages/HomePage.aspx Last accessed September 2012.
  4. Wraith JE, Imrie J. Understanding Niemann-Pick disease type C and its potential treatment. UK Blackwell Publishing, 2007.
  5. Niemann-Pick type C disease: Journey to Diagnosis. A Patient Report. September 2010.