Amyotrophic lateral sclerosis mimic syndromes - A population-based study

Background: The Irish ALS Register is a population-based register of the ep idemiological characteristics of amyotrophic lateral sclerosis (ALS) in the republic of Ireland. Objective: To describe the clinical and demographic details of those patien ts included in the Irish ALS Register who were incorrectly diagnosed as hav ing ALS (patients who were ultimately rediagnosed as having an "ALS mimic s yndrome"). Methods: The medical records of each patient referred to the register are r outinely reviewed and, where possible, patients are examined by our group d uring their illness. Results: Between January 1, 1993, and December 31, 1997, 32 patients (repre senting 7.3% of 437 referrals) were rediagnosed as having a condition other than ALS. The median age at onset for these 32 patients was 56.0 years (ra nge, 19.5-85.8 years) for men and 53.5 years (range, 39.5-70.4 years) for w omen. Twenty-nine patients (91%) presented with symptoms referable to the l imbs, and the remainder presented with symptoms involving the bulbar muscul ature. Multifocal motor neuropathy was the most common condition mistaken f or ALS, accounting for 7 cases (22%), followed closely by Kennedy disease ( 4 cases [13%]). Factors leading to diagnostic revision included evolution o f atypical symptoms, results of specific investigations, and failure of sym ptoms to progress. Twenty-seven (84%) of the patients with an ALS mimic syn drome fulfilled the Fl Escorial criteria for either "suspected" or:"possibl e" ALS, 4 (13%) met the criteria for probable ALS, and 1 (3%) had definite ALS. Conclusions: The application of the El Escorial diagnostic criteria may fac ilitate early recognition of non-ALS cases. Misdiagnosis of ALS remains a c ommon clinical problem despite the increased availability of investigations and a greater awareness among neurologists of potential diagnostic pitfall s.