I read with interest the recent article by Mishra, et al.(1).
They describe an interesting case of distal asymmetric spinal muscular
atrophy involving upper limbs associated with high serum lead levels.
However, I would like to make certain comments.
Firstly, the case presented here has several
features against a diagnosis of Hirayama disease:
1. One year duration of symptoms: A
diagnosis of Hirayama disease is typically made after at least four
to five years of symptoms(2) (after demonstrating a stationary
clinical course following a progressive disease during initial four
to five years of illness),
2. Symmetrical onset of symptoms: Hirayama
disease is characterized by a unilateral-predominant involvement of
upper limbs. Though a bilateral upper limb involvement is seen in
about 20% of cases, it is highly asymmetric, showing a peculiar
"oblique atrophy"(3),
3. Female sex: Hirayama disease is ten
times more common in males(2),
4. Age of six and a half years: The
commonest age of onset is between 15-25 years and onset below 10
years of age has not been reported before.
5. Normal MRI of the spine: MRI
abnormalities are almost universal. In an Indian study, focal cord
atrophy was seen in 100% of cases at the level of cervical 4 to 7
vertebral bodies in MRI done in neutral neck position(4).
Secondly, I disagree with the inclusion of Madras
motor neuron disease (MMND) as a differential diagnosis in this case.
MMND typically presents with the involvement of lower cranial nerves
(seventh and ninth to twelfth) and sensorineural deafness along with
features of chronic anterior horn cell disease(5,6).
The diagnosis in this child could still be a
genetically determined distal spinal muscular atrophy. Genetic and
molecular studies to identify survival motor neuron (SMN) 1 and 2 gene
mutations would have been useful towards making a definite
diagnosis(7).
Finally, the association of elevated serum lead
level in this child appears to be coincidental. However, chelating
therapy is required for the same.
In conclusion, the diagnosis of Hirayama disease
cannot be made confidently in this case. Genetic studies would have
been useful in making a definite diagnosis of spinal muscular atrophy.
Sudhir Kumar,
Department of Neurological Sciences,
Christian Medical College Hospital,
Vellore, Tamilnadu 632 004.
E-mail:
[email protected]
