Ronald F. van Vollenhoven, MD, PhD

Peripheral neuropathy is a fairly common condition in patients with systemic lupus erythematosus (SLE). According to a study by Oomatia et al from 2014,¹ among more than 2,000 patients with SLE, about 6% had peripheral neuropathy, and in the majority this was felt to be related to SLE – an important consideration given that peripheral neuropathy is not uncommon in the population as a whole, and is commonly seen in patients with other diseases that may occur in individuals with SLE as well, especially diabetes mellitus. Thus, peripheral neuropathy can be considered an important neurological manifestation of SLE.

There are major unresolved issues around the treatment of peripheral neuropathy in patients with SLE. While treatment options for peripheral neuropathy in general are quite limited, the fact that this may be a manifestation of SLE would suggest, a prima facie, that some form of lupus-directed therapy could be of benefit. Yet to date there have been very few investigations of this specific question, and no randomised controlled trials. Glucocorticoids, always double-edged in the treatment of chronic diseases, are even more difficult in the case of polyneuropathy, because on the one hand there is the theoretical possibility that they could suppress a direct inflammatory reaction directed against the nerve (but there is no proof of this!), while on the other hand glucocorticoids are associated with peripheral neuropathy as a side-effect, or as a consequence of hyperglycaemia that may be caused or aggravated by the glucocorticoids.

Meanwhile, there are also major issues around the diagnosis of peripheral neuropathy in SLE. This is not truly one disease, as the damage to the nerves may be of different types (axonal, demyelinating, others) or affecting different calibre nerve fibres. The usual investigation is the nerve conduction study (NCS), often combined with electromyogram (EMG), which provides useful information – but there is a legitimate need for other diagnostic tools.

One such tool could be neuromuscular ultrasound (NMUS), the subject of the report by Mahran et al. They investigated 37 patients with SLE who all had peripheral polyneuropathy confirmed by NCS in all but one, and 18 healthy controls. They used a standard ultrasound setup and examined 10 peripheral nerves in each of the subjects, and as the readout they employed the cross-sectional area (CSA) of these nerves. Their findings indicate that in many such patients the CSA may be abnormal – increased in most cases, but also diminished in others.

This innovative report may pave the way for further studies. Important questions will be how NMUS compares to NCS as a diagnostic tool, both in terms of positive and negative predictive value, and whether doing both may provide the best diagnostic yield. Even more interesting will be to see if NMUS can distinguish between different types of peripheral nerve damage and – directly or indirectly – help the clinician in choosing to intervene with immunomodulatory therapy. We are not quite there yet, but this report is an important step in that direction.

 

References

1. Oomatia A, Fang H, Petri M, Birnbaum J. Peripheral neuropathies in systemic lupus erythematosus: clinical features, disease associations, and immunologic characteristics evaluated over a twenty-five-year study period. Arthritis Rheumatol 2014;66:1000–9.