Unless stated otherwise the information below is based on a review in Circulation. It’s a little dated but good, and available as free full text.
What are the differences between HCM as it classically presents in younger patients and HCM of the elderly? Is there such a thing as acquired HCM of the elderly?
Genetic HCM can have its presentation delayed until old age but genetic testing, as opposed to young patients, has a low yield in HCM of the elderly lacking a positive family history.
Certain mutations are known to predispose to later onset disease.
Later onset disease is associated with milder hypertrophy and a more benign course attributable to the disease itself.
Upper septal hypertrophy (USH), aka disproportionate upper septal thickening (DUST) (overlapping with the concept of sigmoid septum) is characteristic though not exclusively seen in the elderly. Its relationship to genetic HCM is unclear but when seen in isolation it is not associated with a bad prognosis.
It is currently believed that an acquired form of HCM, including “IHSS physiology”, can be seen in the elderly, arising from LVH secondary to hypertension or valvular aortic stenosis. The exception is that these patients generally don’t have asymmetric septal hypertrophy (ASH) but rather concentric LVH.
What about the genetics?
A genetic abnormality can be found in most younger patients with HCM and a positive family history.
Up to Date says many mutations have been found in 11 genes.
According to the ACC/AHA guidelines genetic screening has a class IIa recommendation for an index case. Screening of first degree relatives can be clinical (phenotypic) or genetic. Genetic screening to assess the risk of SCD carries only a IIb recommendation. Cost considerations apply in the real world.
What are the anatomic and physiologic variants?
HCM does not always present with the classic “IHSS” phenotype. From my reading of Up to Date, other variants include DUST (which may occur in isolation and not represent HCM, see above), mid septum and free wall hypertrophy resulting in an intracavitay gradient, free wall greater then septal hypertrophy (rare), varying degrees of concentric LVH, and apical HCM (Yamaguchi syndrome).
What are the risk factors for SCD and how should they be taken into account in deciding whether to recommend an AICD?
From the Circulation article:
Accepted risk factors for SCD are unexplained syncope; family history of SCD due to HCM or occurring with no other explanation before 50 years of age; extreme (greater than 30 mm) LVH; ventricular tachycardia, as detected by Holter monitoring; and an abnormal blood pressure response to exercise. Young and middle-aged patients at risk of SCD are usually offered an implantable cardioverter-defibrillator. The risk of SCD may be lower in elderly patients with HCM, but there is uncertainty with regard to how to adapt the conventional risk factors to this population.
These factors are taken together, and a clinical scoring tool is available. Genetic testing to decide on device implantation is not highly recommended.
What are the medical treatments? Where do surgical treatments and septal ablation fit in?
A nice algorithm from the Circulation article is here.