Separating the treatable from the untreatable: a neurologist’s dilemma

My last blog (27th May) was all doom and gloom about having to break bad news to patients. It is not always thus in Neurology. Sometimes the converse happens and you are able to give a patient some unexpectedly good news. I saw a patient recently who had significant muscle weakness and wasting and who was thought to have motor neuron disease (MND). She had been unbelievable stoical in the face of such disastrous news and had resolved to spend her final days contributing to research, managing her affairs for her still very young family and to ensuring that she and her husband went on a cruise around the South Pacific before her death.

However, there was something in the back of my mind that was niggling way. Could it be that she did not have motor neuron disease? She seemed to be a little too stable for too long. She had a number of blood tests and other investigations to look for additional possibilities and all had been negative. Now, we must bear in mind that by the time a neurologists reaches this stage, you are holding out very little hope of finding anything meaningful and the diseases that you are trying to exclude are so fine print that their very mention would draw gasps from one’s colleagues.

In this patient’s case, a repeat set of blood tests disclosed one abnormality that had not turned up the first time round, namely the presence of antibodies to glycosphingolipids, immunologically important compounds that are present on the nerve membrane. The presence of these antibodies does not mean that you do not have motor neuron disease but it does cast some doubt on the diagnosis. In this patient’s case, it was enough to convince me to commence the patient on infusions of intravenous immunoglobulin,a treatment for a condition known as multifocal motor neuropathy with conduction block (MMNCB), a condition that can mimic MND very closely. The patient had more nerve conduction studies, but these did not disclose the typical features of MMNCB. Nevertheless, I said to her that this was the last throw of the dice. She was happy to proceed and we commenced the infusions. After one month, no change. After two months, nothing at all. After 6, perhaps a little if you were trying to be optimistic. After 12 months…OK, there was something going on here. She was responding. Now, 18 months down the track it is clear that she never had MND and that her real diagnosis was MMNCB. There were no faults in the diagnostic process by any of the clinicians that she had seen but it was simply a case of her condition refusing to budge, until the nerve had been thoroughly blasted with IVIG. It also illustrates how important it is to remember that all tests have their false positives and false negatives.

MMNCB can be a very tough diagnosis to make. In this issue of JNNP, there is an interesting paper by Nobile-Orazio and colleagues that outlines a new method of serum assay that may yield a higher detection rate of these antibodies and thereby facilitate a diagnosis of MMNCB http://jnnp.bmj.com/content/85/7/754.abstract. This is an important paper, particularly given that MMNCB is a treatable condition.

So how did our patient react to the change in diagnosis? Well, some patients get very overwhelmed and there have been cases where people have sold their home and spent all their money, thinking that they have a terminal illness, only to be told that they need to finance another 20-30 years of life.

In our patient’s case, no such dramas, just unadulterated joy.

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