Objective: To present a case of McLeod syndrome (MLS) with isolated muscle involvement for many years, which developed late-onset chorea leading to disease diagnosis.

Background: MLS is a very rare genetic X-linked condition due to XK gene mutations. Although chorea is the hallmark of the disease, other features such as psychiatric and cognitive impairment, seizures, cardiomyopathy, muscular involvement and the presence of acanthocytes are common manifestations.

Method: We present a 61-year-old patient with a 20-year history of mild myalgia and elevated creatine kinase (CK), who developed choreic movements at the age of 55. The diagnostic approach, previous to the development of chorea, did not disclose any cause of his muscle disease. Muscle biopsy revealed only mild myopathic changes and a whole-body muscle MRI  showed fatty infiltration in the leg muscles. At examination, the patient showed mild generalized choreic movements and lower limb areflexia. No cognitive or neuropsychiatric alterations were detected.

Results: Brain MRI revealed bilateral atrophy of caudate nuclei. Genetic testing ruled out Huntington’s disease. Peripheral blood smear demonstrated the presence of abundant acanthocytes with weak expression of Kell system antigens. Genetic study of XK gene demonstrated the presence of a nonsense mutation (c.397C>T) at exon 2 leading to a premature stop codon (p.Arg133Ter). Cardiac holter monitoring was normal but cardiac MRI revealed a dilated cardiomyopathy of non-ischemic etiology.

Conclusion: MLS diagnosis is challenging due to the disease rarity and its phenotypic variability. Our case raises the question to consider MLS in patients with isolated long lasting hyperCKemia of unknown etiology even in absence of other clinical features such as chorea, psychiatric symptoms or cardiomyopathy.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/very-long-time-persistent-hyperckemia-as-the-first-manifestation-of-mcleod-syndrome/