Thumb base pain is one of the most common things I evaluate, and it comes from two very different sources that are frequently confused — by patients and, occasionally, by physicians. The first is CMC arthritis, deterioration of the carpometacarpal joint at the very base of the thumb where it meets the wrist. The second is De Quervain's tenosynovitis, inflammation of the tendons that run along the thumb side of the wrist in a tight fibrous tunnel. Both produce pain in roughly the same neighborhood. The distinction matters enormously because the treatments are completely different.

CMC arthritis pain is typically deep and aching, provoked by pinching and gripping — opening jars, turning keys, buttoning shirts. It tends to be a condition of middle age and beyond, significantly more common in women. De Quervain's, on the other hand, produces a sharper, more superficial pain along the thumb side of the wrist, aggravated by movements that sweep the thumb away from the hand — lifting a baby with the thumb extended, scrolling a phone, certain gaming grips. New parents are a classic population for De Quervain's because of the repetitive lifting mechanics involved in caring for an infant.

A useful self-test: the Finkelstein test. Make a fist with your thumb tucked inside your fingers, then tilt your wrist toward your little finger. Sharp pain along the thumb side of the wrist with this maneuver is a strong indicator of De Quervain's. Pain deep at the thumb base with a grinding sensation during a firm pinch points more toward CMC arthritis. Neither replaces an examination, but both give you useful information to bring to the conversation.

De Quervain's tenosynovitis is inflammation of the sheath surrounding two specific tendons — the abductor pollicis longus and extensor pollicis brevis — as they pass through a tight fibrous tunnel on the thumb side of the wrist. Those are the tendons responsible for sweeping the thumb away from the hand and extending it upward. When that tunnel becomes inflamed and thickened, every movement of the thumb through it produces friction, and friction produces pain. In chronic cases the tendon sheath itself becomes so constricted that the tendons move through it with a palpable catching sensation.

What makes De Quervain's particularly interesting clinically is the range of populations it affects. New parents develop it from the repetitive mechanics of lifting an infant with the thumb extended — the load is modest but the frequency is extraordinary, dozens of times per day. Gamers and heavy phone users develop it from sustained thumb abduction against resistance. Fly fishermen are a population I see regularly with this, because the casting motion combined with gripping the rod handle loads those exact tendons in a repetitive pattern over hours on the water.

Treatment starts with activity modification and a thumb spica splint that holds the thumb at rest and removes load from the tendon sheath. This alone resolves a meaningful percentage of cases when adhered to consistently. For cases that don't respond, a precisely placed cortisone injection into the tendon sheath is highly effective — and is one of the situations where I do reach for cortisone with confidence, because the target here is an inflamed sheath, not a degenerating tendon. Next week we go deeper into why it happens and, more usefully, how to prevent it before it starts.

Last week I made the case for thinking about footwear as a medical decision. The same logic applies to thermal protection, and with equal stakes in the environments we are heading into. The Alaskan coastal climate combines factors that make thermal management genuinely unforgiving: ambient temperatures in the range where the body works hard to maintain core temperature, high humidity that saturates insulating layers, precipitation that arrives without warning, and wind that accelerates heat loss at a rate most people significantly underestimate. Cotton in this environment is not a style mistake. It is a physiological one — it absorbs moisture, loses all insulating value when wet, and sits against the skin as a cold, damp surface while the body struggles to compensate.

The base layer is the element most people underinvest in, and it is the one that matters most. Its job is moisture management — moving perspiration away from the skin surface so it does not rob the body of heat through evaporative cooling. Merino wool and certain synthetic fabrics do this effectively even when partially saturated. The mid layer provides the thermal value, but only if the base layer has kept the skin surface dry enough to allow it to function. The outer layer manages wind and precipitation. These three functions work as a system, and breaking the chain at any link costs you the whole thing.

For a multi-generational trip spanning four people across four decades of age, this planning cannot be one-size-fits-all. Thermoregulation changes with age — older adults have reduced peripheral circulation and a diminished shiver response, both of which affect how quickly and efficiently the body responds to cold stress. A 58-year-old and a 16-year-old in the same ambient conditions are not having the same physiological experience, and the layering system needs to account for that. I will continue building out this framework in the coming weeks before our late May departure.