Vital capacity in spinal muscular atrophy

This work describes and correlates plateau/maximum observed vital capacity (VC) with spinal muscular atrophy (SMA) severity and prognosis for autonomous breathing.

SMA severity was correlated with VC, onset, paradoxical breathing, age at definitive dependence on continuous mechanical ventilation (DDCV), and age at first respiratory hospitalization and gastrostomy.

Ten severe SMA 1A patients with DDCV before 6 mos of age had maximum observed and plateau VC of 100 ml or less, with plateaus for six at 10.3 (range, 3-48) mos. Another 120 had typical SMA 1B defined by any three of the following: acute respiratory failure before 12 mos of age, gastrostomy before 12 mos of age, DDCV before 10 yrs of age, and VC not exceeding 200 ml, with plateaus for 15 at 26.4 (6-138) mos. Fifteen were with mild type 1C defined by three of the following: VC exceeding 200 ml, acute respiratory failure after 1 yr of age, gastrostomy after 1 yr of age, and no DDCV before 10 yrs of age and had a plateau/maximum observed mean VC of 409 (range, 200-1175) ml at 8.9 (range, 7-10) yrs of age. Of 88 patients with SMA 2 and paradoxical breathing (2A), 16 had a mean plateau/maximum observed VC of 758 (range, 460-2100) ml. DDCV with no autonomous breathing always followed plateauing of VC. Types 2B, 3, and 4 patients attained normal VC. Intergroup VC differences were significant (P < 0.05) for 1A, 1B, 1C, 2A, and 2B-4. When intubated and "unweanable," 50-ml VC signaled the ability for autonomous breathing 1 to 21 days after extubation.

VC should be monitored from birth. It correlates with prognosis with SMA 1A VCs not exceeding 100 ml or 1B 200 ml. Patients who attained 200 ml at any time (milder 1C) retain some ability to breathe after 10 yrs of age.