Wasting of First Dorsal Interossei (small muscles of hand)

In the picture above, you can see a depression in the first web space (between thumb and index finger). This is suggestive of wasting of first dorsal interosseous (FDI) muscles. This patient had bilateral C8-T1 lesion.

Small muscle wasting can have varied localizations: Lower cervical cord lesion, anterior horn cell disease, C8-T1 root lesion, lower trunk plexopathy and ulnar nerve lesion. Careful clinical examination is required, before investigations such as MRI cervical spine, nerve conduction studies and EMG can be ordered for.

Split hand sign: It is specific for amyotrophic lateral sclerosis (ALS). In ALS, there is wasting of FDI muscles, associated with thenar muscle wasting. However, hypothenar muscles are relatively spared. See the picture below (source: Med J DY Patil Univ)

Published by Dr Sudhir Kumar MD (Medicine) DM (Neurology)

I am a doctor with 25 years experience. I have worked as a neurologist for about 20 years. Educating public and healthcare professionals is very dear to me. This is possible due to my interactions with thousands of patients and their caregivers. I salute the patients who suffer and it is our duty to minimise suffering by preventing diseases and ensuring prompt diagnosis and treatment of those already affected.

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