Leg amyotrophic diplegia: prevalence and pattern of weakness at US neuromuscular centers

To identify the frequency of leg amyotrophic diplegia (LAD) at a US academic center, describe the pattern of weakness, and provide comparative data from 8 additional major US academic institutions.

LAD is a leg onset variant of progressive muscular atrophy (PMA). LAD weakness is confined to the legs for at least 2 years, and there are no upper motor neuron signs.

We present a retrospective chart review of 24 patients with the LAD presentation from the University of Kansas Medical Center ( n = 8 cases) and from 8 US academic institutions (n = 16 cases).

Of the 318 subjects identified in the University of Kansas Medical Center Neuromuscular Research Database, 82% (260 subjects) had amyotrophic lateral sclerosis (ALS), 1.9% (6) had familial ALS, 6.6% (21) had primary lateral sclerosis, and 9.2% (29) had lower motor neuron (LMN) disease. Of these 29 cases, 16 had PMA, 5 had brachial amyotrophic diplegia, while 8 had LAD. The mean LAD age of onset was 58 years with a male/female ratio of 3/1. Onset was asymmetric in 7/8. We identified a pelviperoneal pattern of weakness (sparing of knee extension and/or ankle plantar flexion) in 4 cases and distal predominant weakness in 3 cases. All patients had electrodiagnostic findings consistent with motor neuron disease confined to the lower extremities. We present LAD disease duration and survival data from 8 major academic neuromuscular centers. At last follow-up, weakness progressed to involve the arms in 6/24 LAD cases and of these 6 cases, 2 patients died from progression to typical ALS. From onset of symptoms, mean survival in LAD is 87 months, with 92% of cases being alive.

The natural history of LAD differs from typical forms of ALS and PMA. LAD is a slowly progressive disorder that accounts for a fourth of LMN disease cases. An asymmetric pelviperoneal pattern of weakness should heighten the suspicion for LAD.