Truncal ataxia or disequilibrium is an unrecognised cause of orthostatic intolerance in patients with myalgic encephalomyelitis.

Abstract

Chronic fatigue syndrome (CFS) causes a marked reduction in the activities of daily living and impairs the quality of life. Recently, dysfunction of the central nervous system associated with myalgic encephalomyelitis (ME) has been postulated as the main cause of CFS.1 Most patients with ME/CFS have orthostatic intolerance (OI) which is the primary factor restricting the daily functional capacity and in turn quality of life.2-4 OI is characterised by the inability to remain upright without severe signs and symptoms, such as hypotension, tachycardia, light-headedness, pallor, fatigue, weakness, dizziness, diminished concentration, tremulousness and nausea. Most symptoms of OI have been surmised to be related to reduced cerebral blood flow with or without impaired cerebral circulatory autoregulation, and the compensatory activation of the sympathetic nervous system.5, 6 Indeed, many patients have postural orthostatic tachycardia, delayed orthostatic hypotension and neurally mediated hypotension.4, 5, 7-9 Also many patients have low cardiac output in association with a small left ventricle.10-12 With further progression of the disease, patients may have even sitting intolerance and finally become bedridden. Although static balance is an essential element for the performance of daily activities as well as postural stability, the possible relation between disequilibrium and OI has never been investigated. The possible role of static or truncal ataxia in the genesis of both orthostatic and sitting intolerance was examined in patients with ME. Myalgic encephalomyelitis was diagnosed according to the International Consensus Criteria proposed in 2011.1 The study subjects comprising 35 patients with ME (8 men and 27 women, mean age: 36±10 years), underwent both the conventional 10-min standing and sitting tests3 separately and also neurological examinations. Symptoms of OI was noted in 33 (94%) patients during the standing test and sitting intolerance in 25 (71%) during the sitting test. Romberg test was performed by having the patient stand with his/her feet together and eyes shut. When this caused the instability to worsen markedly, producing wide oscillations and possibly a fall, the Romberg test was positive. The patients were divided into 10 (29%) with a positive Romberg test (P) and 25 (71%) with a negative one (N). Among the patients with a positive Romberg test, five (50%) had some instability on standing with their feet together and even eyes open, which worsened markedly with eyes shut. Comparative data between the patients with a positive and negative Romberg test are summarised in Table 1. The disease history length was not significantly different between the groups. None of P was able to stand on one-leg or had normal tandem gait. Almost all P complained of symptoms during both the standing and sitting tests in which many (40%) failed to complete the 10-min standing, and some (20%) not even 10-min sitting. In contrast, almost all N were able to stand on one-leg, demonstrated smooth tandem gait and completed both the tests. Postural sway was observed during the standing test in all of P in contrast to 5 (20%) of N. P had higher performance status scores9 than N, suggesting severe restriction of the activities of daily living. Although contradictory results have been reported concerning disequilibrium in patients with CFS,13, 14 in the present study the standard neurological examination demonstrated abnormal results such as a positive Romberg test, impaired one-leg standing and unstable tandem gait, suggesting disequilibrium or truncal ataxia in a considerable number of the patients with ME. In conclusion, patients with ME and a positive Romberg test predominantly complain of not only OI but also sitting intolerance. Postural reflex dysfunction associated with disequilibrium appears to play an important role in the genesis of the postural intolerance. Truncal ataxia or disequilibrium is an unrecognised but important cause of OI in the patients. A positive Romberg test is a useful sign for advanced disease. We thank Ms. Takako Miwa for her technical help. This work was supported in part by JAPS KAKENHI (grant number 15H00649). The authors declare that there is no conflict of interest.